crypto/async_tx/async_pq.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /*
  * Copyright(c) 2007 Yuri Tikhonov <yur@emcraft.com>
  * Copyright(c) 2009 Intel Corporation
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation; either version 2 of the License, or (at your option)
  * any later version.
  *
  * This program is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  * more details.
  *
  * You should have received a copy of the GNU General Public License along with
  * this program; if not, write to the Free Software Foundation, Inc., 59
  * Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  *
  * The full GNU General Public License is included in this distribution in the
  * file called COPYING.
  */
 #include <linux/kernel.h>
 #include <linux/interrupt.h>
 #include <linux/dma-mapping.h>
 #include <linux/raid/pq.h>
 #include <linux/async_tx.h>

 /**
  * scribble - space to hold throwaway P buffer for synchronous gen_syndrome
  */
 static struct page *scribble;

 static bool is_raid6_zero_block(struct page *p)
 {
 	return p == (void *) raid6_empty_zero_page;
 }

 /* the struct page *blocks[] parameter passed to async_gen_syndrome()
  * and async_syndrome_val() contains the 'P' destination address at
  * blocks[disks-2] and the 'Q' destination address at blocks[disks-1]
  *
  * note: these are macros as they are used as lvalues
  */
 #define P(b, d) (b[d-2])
 #define Q(b, d) (b[d-1])

 /**
  * do_async_gen_syndrome - asynchronously calculate P and/or Q
  */
 static __async_inline struct dma_async_tx_descriptor *
 do_async_gen_syndrome(struct dma_chan *chan, struct page **blocks,
 		      const unsigned char *scfs, unsigned int offset, int disks,
 		      size_t len, dma_addr_t *dma_src,
 		      struct async_submit_ctl *submit)
 {
 	struct dma_async_tx_descriptor *tx = NULL;
 	struct dma_device *dma = chan->device;
 	enum dma_ctrl_flags dma_flags = 0;
 	enum async_tx_flags flags_orig = submit->flags;
 	dma_async_tx_callback cb_fn_orig = submit->cb_fn;
 	dma_async_tx_callback cb_param_orig = submit->cb_param;
 	int src_cnt = disks - 2;
 	unsigned char coefs[src_cnt];
 	unsigned short pq_src_cnt;
 	dma_addr_t dma_dest[2];
 	int src_off = 0;
 	int idx;
 	int i;

 	/* DMAs use destinations as sources, so use BIDIRECTIONAL mapping */
 	if (P(blocks, disks))
 		dma_dest[0] = dma_map_page(dma->dev, P(blocks, disks), offset,
 					   len, DMA_BIDIRECTIONAL);
 	else
 		dma_flags |= DMA_PREP_PQ_DISABLE_P;
 	if (Q(blocks, disks))
 		dma_dest[1] = dma_map_page(dma->dev, Q(blocks, disks), offset,
 					   len, DMA_BIDIRECTIONAL);
 	else
 		dma_flags |= DMA_PREP_PQ_DISABLE_Q;

 	/* convert source addresses being careful to collapse 'empty'
 	 * sources and update the coefficients accordingly
 	 */
 	for (i = 0, idx = 0; i < src_cnt; i++) {
 		if (is_raid6_zero_block(blocks[i]))
 			continue;
 		dma_src[idx] = dma_map_page(dma->dev, blocks[i], offset, len,
 					    DMA_TO_DEVICE);
 		coefs[idx] = scfs[i];
 		idx++;
 	}
 	src_cnt = idx;

 	while (src_cnt > 0) {
 		submit->flags = flags_orig;
 		pq_src_cnt = min(src_cnt, dma_maxpq(dma, dma_flags));
 		/* if we are submitting additional pqs, leave the chain open,
 		 * clear the callback parameters, and leave the destination
 		 * buffers mapped
 		 */
 		if (src_cnt > pq_src_cnt) {
 			submit->flags &= ~ASYNC_TX_ACK;
 			submit->flags |= ASYNC_TX_FENCE;
 			dma_flags |= DMA_COMPL_SKIP_DEST_UNMAP;
 			submit->cb_fn = NULL;
 			submit->cb_param = NULL;
 		} else {
 			dma_flags &= ~DMA_COMPL_SKIP_DEST_UNMAP;
 			submit->cb_fn = cb_fn_orig;
 			submit->cb_param = cb_param_orig;
 			if (cb_fn_orig)
 				dma_flags |= DMA_PREP_INTERRUPT;
 		}
 		if (submit->flags & ASYNC_TX_FENCE)
 			dma_flags |= DMA_PREP_FENCE;

 		/* Since we have clobbered the src_list we are committed
 		 * to doing this asynchronously.  Drivers force forward
 		 * progress in case they can not provide a descriptor
 		 */
 		for (;;) {
 			tx = dma->device_prep_dma_pq(chan, dma_dest,
 						     &dma_src[src_off],
 						     pq_src_cnt,
 						     &coefs[src_off], len,
 						     dma_flags);
 			if (likely(tx))
 				break;
 			async_tx_quiesce(&submit->depend_tx);
 			dma_async_issue_pending(chan);
 		}

 		async_tx_submit(chan, tx, submit);
 		submit->depend_tx = tx;

 		/* drop completed sources */
 		src_cnt -= pq_src_cnt;
 		src_off += pq_src_cnt;

 		dma_flags |= DMA_PREP_CONTINUE;
 	}

 	return tx;
 }

 /**
  * do_sync_gen_syndrome - synchronously calculate a raid6 syndrome
  */
 static void
 do_sync_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
 		     size_t len, struct async_submit_ctl *submit)
 {
 	void **srcs;
 	int i;

 	if (submit->scribble)
 		srcs = submit->scribble;
 	else
 		srcs = (void **) blocks;

 	for (i = 0; i < disks; i++) {
 		if (is_raid6_zero_block(blocks[i])) {
 			BUG_ON(i > disks - 3); /* P or Q can't be zero */
 			srcs[i] = blocks[i];
 		} else
 			srcs[i] = page_address(blocks[i]) + offset;
 	}
 	raid6_call.gen_syndrome(disks, len, srcs);
 	async_tx_sync_epilog(submit);
 }

 /**
  * async_gen_syndrome - asynchronously calculate a raid6 syndrome
  * @blocks: source blocks from idx 0..disks-3, P @ disks-2 and Q @ disks-1
  * @offset: common offset into each block (src and dest) to start transaction
  * @disks: number of blocks (including missing P or Q, see below)
  * @len: length of operation in bytes
  * @submit: submission/completion modifiers
  *
  * General note: This routine assumes a field of GF(2^8) with a
  * primitive polynomial of 0x11d and a generator of {02}.
  *
  * 'disks' note: callers can optionally omit either P or Q (but not
  * both) from the calculation by setting blocks[disks-2] or
  * blocks[disks-1] to NULL.  When P or Q is omitted 'len' must be <=
  * PAGE_SIZE as a temporary buffer of this size is used in the
  * synchronous path.  'disks' always accounts for both destination
  * buffers.
  *
  * 'blocks' note: if submit->scribble is NULL then the contents of
  * 'blocks' may be overridden
  */
 struct dma_async_tx_descriptor *
 async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
 		   size_t len, struct async_submit_ctl *submit)
 {
 	int src_cnt = disks - 2;
 	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
 						      &P(blocks, disks), 2,
 						      blocks, src_cnt, len);
 	struct dma_device *device = chan ? chan->device : NULL;
 	dma_addr_t *dma_src = NULL;

 	BUG_ON(disks > 255 || !(P(blocks, disks) || Q(blocks, disks)));

 	if (submit->scribble)
 		dma_src = submit->scribble;
 	else if (sizeof(dma_addr_t) <= sizeof(struct page *))
 		dma_src = (dma_addr_t *) blocks;

 	if (dma_src && device &&
 	    (src_cnt <= dma_maxpq(device, 0) ||
 	     dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
 	    is_dma_pq_aligned(device, offset, 0, len)) {
 		/* run the p+q asynchronously */
 		pr_debug("%s: (async) disks: %d len: %zu\n",
 			 __func__, disks, len);
 		return do_async_gen_syndrome(chan, blocks, raid6_gfexp, offset,
 					     disks, len, dma_src, submit);
 	}

 	/* run the pq synchronously */
 	pr_debug("%s: (sync) disks: %d len: %zu\n", __func__, disks, len);

 	/* wait for any prerequisite operations */
 	async_tx_quiesce(&submit->depend_tx);

 	if (!P(blocks, disks)) {
 		P(blocks, disks) = scribble;
 		BUG_ON(len + offset > PAGE_SIZE);
 	}
 	if (!Q(blocks, disks)) {
 		Q(blocks, disks) = scribble;
 		BUG_ON(len + offset > PAGE_SIZE);
 	}
 	do_sync_gen_syndrome(blocks, offset, disks, len, submit);

 	return NULL;
 }
 EXPORT_SYMBOL_GPL(async_gen_syndrome);

 /**
  * async_syndrome_val - asynchronously validate a raid6 syndrome
  * @blocks: source blocks from idx 0..disks-3, P @ disks-2 and Q @ disks-1
  * @offset: common offset into each block (src and dest) to start transaction
  * @disks: number of blocks (including missing P or Q, see below)
  * @len: length of operation in bytes
  * @pqres: on val failure SUM_CHECK_P_RESULT and/or SUM_CHECK_Q_RESULT are set
  * @spare: temporary result buffer for the synchronous case
  * @submit: submission / completion modifiers
  *
  * The same notes from async_gen_syndrome apply to the 'blocks',
  * and 'disks' parameters of this routine.  The synchronous path
  * requires a temporary result buffer and submit->scribble to be
  * specified.
  */
 struct dma_async_tx_descriptor *
 async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
 		   size_t len, enum sum_check_flags *pqres, struct page *spare,
 		   struct async_submit_ctl *submit)
 {
 	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ_VAL,
 						      NULL, 0,  blocks, disks,
 						      len);
 	struct dma_device *device = chan ? chan->device : NULL;
 	struct dma_async_tx_descriptor *tx;
 	enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
 	dma_addr_t *dma_src = NULL;

 	BUG_ON(disks < 4);

 	if (submit->scribble)
 		dma_src = submit->scribble;
 	else if (sizeof(dma_addr_t) <= sizeof(struct page *))
 		dma_src = (dma_addr_t *) blocks;

 	if (dma_src && device && disks <= dma_maxpq(device, 0) &&
 	    is_dma_pq_aligned(device, offset, 0, len)) {
 		struct device *dev = device->dev;
 		dma_addr_t *pq = &dma_src[disks-2];
 		int i;

 		pr_debug("%s: (async) disks: %d len: %zu\n",
 			 __func__, disks, len);
 		if (!P(blocks, disks))
 			dma_flags |= DMA_PREP_PQ_DISABLE_P;
 		if (!Q(blocks, disks))
 			dma_flags |= DMA_PREP_PQ_DISABLE_Q;
 		if (submit->flags & ASYNC_TX_FENCE)
 			dma_flags |= DMA_PREP_FENCE;
 		for (i = 0; i < disks; i++)
 			if (likely(blocks[i])) {
 				BUG_ON(is_raid6_zero_block(blocks[i]));
 				dma_src[i] = dma_map_page(dev, blocks[i],
 							  offset, len,
 							  DMA_TO_DEVICE);
 			}

 		for (;;) {
 			tx = device->device_prep_dma_pq_val(chan, pq, dma_src,
 							    disks - 2,
 							    raid6_gfexp,
 							    len, pqres,
 							    dma_flags);
 			if (likely(tx))
 				break;
 			async_tx_quiesce(&submit->depend_tx);
 			dma_async_issue_pending(chan);
 		}
 		async_tx_submit(chan, tx, submit);

 		return tx;
 	} else {
 		struct page *p_src = P(blocks, disks);
 		struct page *q_src = Q(blocks, disks);
 		enum async_tx_flags flags_orig = submit->flags;
 		dma_async_tx_callback cb_fn_orig = submit->cb_fn;
 		void *scribble = submit->scribble;
 		void *cb_param_orig = submit->cb_param;
 		void *p, *q, *s;

 		pr_debug("%s: (sync) disks: %d len: %zu\n",
 			 __func__, disks, len);

 		/* caller must provide a temporary result buffer and
 		 * allow the input parameters to be preserved
 		 */
 		BUG_ON(!spare || !scribble);

 		/* wait for any prerequisite operations */
 		async_tx_quiesce(&submit->depend_tx);

 		/* recompute p and/or q into the temporary buffer and then
 		 * check to see the result matches the current value
 		 */
 		tx = NULL;
 		*pqres = 0;
 		if (p_src) {
 			init_async_submit(submit, ASYNC_TX_XOR_ZERO_DST, NULL,
 					  NULL, NULL, scribble);
 			tx = async_xor(spare, blocks, offset, disks-2, len, submit);
 			async_tx_quiesce(&tx);
 			p = page_address(p_src) + offset;
 			s = page_address(spare) + offset;
 			*pqres |= !!memcmp(p, s, len) << SUM_CHECK_P;
 		}

 		if (q_src) {
 			P(blocks, disks) = NULL;
 			Q(blocks, disks) = spare;
 			init_async_submit(submit, 0, NULL, NULL, NULL, scribble);
 			tx = async_gen_syndrome(blocks, offset, disks, len, submit);
 			async_tx_quiesce(&tx);
 			q = page_address(q_src) + offset;
 			s = page_address(spare) + offset;
 			*pqres |= !!memcmp(q, s, len) << SUM_CHECK_Q;
 		}

 		/* restore P, Q and submit */
 		P(blocks, disks) = p_src;
 		Q(blocks, disks) = q_src;

 		submit->cb_fn = cb_fn_orig;
 		submit->cb_param = cb_param_orig;
 		submit->flags = flags_orig;
 		async_tx_sync_epilog(submit);

 		return NULL;
 	}
 }
 EXPORT_SYMBOL_GPL(async_syndrome_val);

 static int __init async_pq_init(void)
 {
 	scribble = alloc_page(GFP_KERNEL);

 	if (scribble)
 		return 0;

 	pr_err("%s: failed to allocate required spare page\n", __func__);

 	return -ENOMEM;
 }

 static void __exit async_pq_exit(void)
 {
 	put_page(scribble);
 }

 module_init(async_pq_init);
 module_exit(async_pq_exit);

 MODULE_DESCRIPTION("asynchronous raid6 syndrome generation/validation");
 MODULE_LICENSE("GPL");
	/*
	* Copyright(c) 2007 Yuri Tikhonov <yur@emcraft.com>
	* Copyright(c) 2009 Intel Corporation
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License as published by the Free
	* Software Foundation; either version 2 of the License, or (at your option)
	* any later version.
	*
	* This program is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	* more details.
	*
	* You should have received a copy of the GNU General Public License along with
	* this program; if not, write to the Free Software Foundation, Inc., 59
	* Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	*
	* The full GNU General Public License is included in this distribution in the
	* file called COPYING.
	*/
	#include <linux/kernel.h>
	#include <linux/interrupt.h>
	#include <linux/dma-mapping.h>
	#include <linux/raid/pq.h>
	#include <linux/async_tx.h>

	/**
	* scribble - space to hold throwaway P buffer for synchronous gen_syndrome
	*/
	static struct page *scribble;

	static bool is_raid6_zero_block(struct page *p)
	{
	return p == (void *) raid6_empty_zero_page;
	}

	/* the struct page *blocks[] parameter passed to async_gen_syndrome()
	* and async_syndrome_val() contains the 'P' destination address at
	* blocks[disks-2] and the 'Q' destination address at blocks[disks-1]
	*
	* note: these are macros as they are used as lvalues
	*/
	#define P(b, d) (b[d-2])
	#define Q(b, d) (b[d-1])

	/**
	* do_async_gen_syndrome - asynchronously calculate P and/or Q
	*/
	static __async_inline struct dma_async_tx_descriptor *
	do_async_gen_syndrome(struct dma_chan chan, struct page *blocks,
	const unsigned char *scfs, unsigned int offset, int disks,
	size_t len, dma_addr_t *dma_src,
	struct async_submit_ctl *submit)
	{
	struct dma_async_tx_descriptor *tx = NULL;
	struct dma_device *dma = chan->device;
	enum dma_ctrl_flags dma_flags = 0;
	enum async_tx_flags flags_orig = submit->flags;
	dma_async_tx_callback cb_fn_orig = submit->cb_fn;
	dma_async_tx_callback cb_param_orig = submit->cb_param;
	int src_cnt = disks - 2;
	unsigned char coefs[src_cnt];
	unsigned short pq_src_cnt;
	dma_addr_t dma_dest[2];
	int src_off = 0;
	int idx;
	int i;

	/* DMAs use destinations as sources, so use BIDIRECTIONAL mapping */
	if (P(blocks, disks))
	dma_dest[0] = dma_map_page(dma->dev, P(blocks, disks), offset,
	len, DMA_BIDIRECTIONAL);
	else
	dma_flags \|= DMA_PREP_PQ_DISABLE_P;
	if (Q(blocks, disks))
	dma_dest[1] = dma_map_page(dma->dev, Q(blocks, disks), offset,
	len, DMA_BIDIRECTIONAL);
	else
	dma_flags \|= DMA_PREP_PQ_DISABLE_Q;

	/* convert source addresses being careful to collapse 'empty'
	* sources and update the coefficients accordingly
	*/
	for (i = 0, idx = 0; i < src_cnt; i++) {
	if (is_raid6_zero_block(blocks[i]))
	continue;
	dma_src[idx] = dma_map_page(dma->dev, blocks[i], offset, len,
	DMA_TO_DEVICE);
	coefs[idx] = scfs[i];
	idx++;
	}
	src_cnt = idx;

	while (src_cnt > 0) {
	submit->flags = flags_orig;
	pq_src_cnt = min(src_cnt, dma_maxpq(dma, dma_flags));
	/* if we are submitting additional pqs, leave the chain open,
	* clear the callback parameters, and leave the destination
	* buffers mapped
	*/
	if (src_cnt > pq_src_cnt) {
	submit->flags &= ~ASYNC_TX_ACK;
	submit->flags \|= ASYNC_TX_FENCE;
	dma_flags \|= DMA_COMPL_SKIP_DEST_UNMAP;
	submit->cb_fn = NULL;
	submit->cb_param = NULL;
	} else {
	dma_flags &= ~DMA_COMPL_SKIP_DEST_UNMAP;
	submit->cb_fn = cb_fn_orig;
	submit->cb_param = cb_param_orig;
	if (cb_fn_orig)
	dma_flags \|= DMA_PREP_INTERRUPT;
	}
	if (submit->flags & ASYNC_TX_FENCE)
	dma_flags \|= DMA_PREP_FENCE;

	/* Since we have clobbered the src_list we are committed
	* to doing this asynchronously. Drivers force forward
	* progress in case they can not provide a descriptor
	*/
	for (;;) {
	tx = dma->device_prep_dma_pq(chan, dma_dest,
	&dma_src[src_off],
	pq_src_cnt,
	&coefs[src_off], len,
	dma_flags);
	if (likely(tx))
	break;
	async_tx_quiesce(&submit->depend_tx);
	dma_async_issue_pending(chan);
	}

	async_tx_submit(chan, tx, submit);
	submit->depend_tx = tx;

	/* drop completed sources */
	src_cnt -= pq_src_cnt;
	src_off += pq_src_cnt;

	dma_flags \|= DMA_PREP_CONTINUE;
	}

	return tx;
	}

	/**
	* do_sync_gen_syndrome - synchronously calculate a raid6 syndrome
	*/
	static void
	do_sync_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
	size_t len, struct async_submit_ctl *submit)
	{
	void **srcs;
	int i;

	if (submit->scribble)
	srcs = submit->scribble;
	else
	srcs = (void **) blocks;

	for (i = 0; i < disks; i++) {
	if (is_raid6_zero_block(blocks[i])) {
	BUG_ON(i > disks - 3); /* P or Q can't be zero */
	srcs[i] = blocks[i];
	} else
	srcs[i] = page_address(blocks[i]) + offset;
	}
	raid6_call.gen_syndrome(disks, len, srcs);
	async_tx_sync_epilog(submit);
	}

	/**
	* async_gen_syndrome - asynchronously calculate a raid6 syndrome
	* @blocks: source blocks from idx 0..disks-3, P @ disks-2 and Q @ disks-1
	* @offset: common offset into each block (src and dest) to start transaction
	* @disks: number of blocks (including missing P or Q, see below)
	* @len: length of operation in bytes
	* @submit: submission/completion modifiers
	*
	* General note: This routine assumes a field of GF(2^8) with a
	* primitive polynomial of 0x11d and a generator of {02}.
	*
	* 'disks' note: callers can optionally omit either P or Q (but not
	* both) from the calculation by setting blocks[disks-2] or
	* blocks[disks-1] to NULL. When P or Q is omitted 'len' must be <=
	* PAGE_SIZE as a temporary buffer of this size is used in the
	* synchronous path. 'disks' always accounts for both destination
	* buffers.
	*
	* 'blocks' note: if submit->scribble is NULL then the contents of
	* 'blocks' may be overridden
	*/
	struct dma_async_tx_descriptor *
	async_gen_syndrome(struct page **blocks, unsigned int offset, int disks,
	size_t len, struct async_submit_ctl *submit)
	{
	int src_cnt = disks - 2;
	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ,
	&P(blocks, disks), 2,
	blocks, src_cnt, len);
	struct dma_device *device = chan ? chan->device : NULL;
	dma_addr_t *dma_src = NULL;

	BUG_ON(disks > 255 \|\| !(P(blocks, disks) \|\| Q(blocks, disks)));

	if (submit->scribble)
	dma_src = submit->scribble;
	else if (sizeof(dma_addr_t) <= sizeof(struct page *))
	dma_src = (dma_addr_t *) blocks;

	if (dma_src && device &&
	(src_cnt <= dma_maxpq(device, 0) \|\|
	dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
	is_dma_pq_aligned(device, offset, 0, len)) {
	/* run the p+q asynchronously */
	pr_debug("%s: (async) disks: %d len: %zu\n",
	__func__, disks, len);
	return do_async_gen_syndrome(chan, blocks, raid6_gfexp, offset,
	disks, len, dma_src, submit);
	}

	/* run the pq synchronously */
	pr_debug("%s: (sync) disks: %d len: %zu\n", __func__, disks, len);

	/* wait for any prerequisite operations */
	async_tx_quiesce(&submit->depend_tx);

	if (!P(blocks, disks)) {
	P(blocks, disks) = scribble;
	BUG_ON(len + offset > PAGE_SIZE);
	}
	if (!Q(blocks, disks)) {
	Q(blocks, disks) = scribble;
	BUG_ON(len + offset > PAGE_SIZE);
	}
	do_sync_gen_syndrome(blocks, offset, disks, len, submit);

	return NULL;
	}
	EXPORT_SYMBOL_GPL(async_gen_syndrome);

	/**
	* async_syndrome_val - asynchronously validate a raid6 syndrome
	* @blocks: source blocks from idx 0..disks-3, P @ disks-2 and Q @ disks-1
	* @offset: common offset into each block (src and dest) to start transaction
	* @disks: number of blocks (including missing P or Q, see below)
	* @len: length of operation in bytes
	* @pqres: on val failure SUM_CHECK_P_RESULT and/or SUM_CHECK_Q_RESULT are set
	* @spare: temporary result buffer for the synchronous case
	* @submit: submission / completion modifiers
	*
	* The same notes from async_gen_syndrome apply to the 'blocks',
	* and 'disks' parameters of this routine. The synchronous path
	* requires a temporary result buffer and submit->scribble to be
	* specified.
	*/
	struct dma_async_tx_descriptor *
	async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
	size_t len, enum sum_check_flags pqres, struct page spare,
	struct async_submit_ctl *submit)
	{
	struct dma_chan *chan = async_tx_find_channel(submit, DMA_PQ_VAL,
	NULL, 0, blocks, disks,
	len);
	struct dma_device *device = chan ? chan->device : NULL;
	struct dma_async_tx_descriptor *tx;
	enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
	dma_addr_t *dma_src = NULL;

	BUG_ON(disks < 4);

	if (submit->scribble)
	dma_src = submit->scribble;
	else if (sizeof(dma_addr_t) <= sizeof(struct page *))
	dma_src = (dma_addr_t *) blocks;

	if (dma_src && device && disks <= dma_maxpq(device, 0) &&
	is_dma_pq_aligned(device, offset, 0, len)) {
	struct device *dev = device->dev;
	dma_addr_t *pq = &dma_src[disks-2];
	int i;

	pr_debug("%s: (async) disks: %d len: %zu\n",
	__func__, disks, len);
	if (!P(blocks, disks))
	dma_flags \|= DMA_PREP_PQ_DISABLE_P;
	if (!Q(blocks, disks))
	dma_flags \|= DMA_PREP_PQ_DISABLE_Q;
	if (submit->flags & ASYNC_TX_FENCE)
	dma_flags \|= DMA_PREP_FENCE;
	for (i = 0; i < disks; i++)
	if (likely(blocks[i])) {
	BUG_ON(is_raid6_zero_block(blocks[i]));
	dma_src[i] = dma_map_page(dev, blocks[i],
	offset, len,
	DMA_TO_DEVICE);
	}

	for (;;) {
	tx = device->device_prep_dma_pq_val(chan, pq, dma_src,
	disks - 2,
	raid6_gfexp,
	len, pqres,
	dma_flags);
	if (likely(tx))
	break;
	async_tx_quiesce(&submit->depend_tx);
	dma_async_issue_pending(chan);
	}
	async_tx_submit(chan, tx, submit);

	return tx;
	} else {
	struct page *p_src = P(blocks, disks);
	struct page *q_src = Q(blocks, disks);
	enum async_tx_flags flags_orig = submit->flags;
	dma_async_tx_callback cb_fn_orig = submit->cb_fn;
	void *scribble = submit->scribble;
	void *cb_param_orig = submit->cb_param;
	void p, q, *s;

	pr_debug("%s: (sync) disks: %d len: %zu\n",
	__func__, disks, len);

	/* caller must provide a temporary result buffer and
	* allow the input parameters to be preserved
	*/
	BUG_ON(!spare \|\| !scribble);

	/* wait for any prerequisite operations */
	async_tx_quiesce(&submit->depend_tx);

	/* recompute p and/or q into the temporary buffer and then
	* check to see the result matches the current value
	*/
	tx = NULL;
	*pqres = 0;
	if (p_src) {
	init_async_submit(submit, ASYNC_TX_XOR_ZERO_DST, NULL,
	NULL, NULL, scribble);
	tx = async_xor(spare, blocks, offset, disks-2, len, submit);
	async_tx_quiesce(&tx);
	p = page_address(p_src) + offset;
	s = page_address(spare) + offset;
	*pqres \|= !!memcmp(p, s, len) << SUM_CHECK_P;
	}

	if (q_src) {
	P(blocks, disks) = NULL;
	Q(blocks, disks) = spare;
	init_async_submit(submit, 0, NULL, NULL, NULL, scribble);
	tx = async_gen_syndrome(blocks, offset, disks, len, submit);
	async_tx_quiesce(&tx);
	q = page_address(q_src) + offset;
	s = page_address(spare) + offset;
	*pqres \|= !!memcmp(q, s, len) << SUM_CHECK_Q;
	}

	/* restore P, Q and submit */
	P(blocks, disks) = p_src;
	Q(blocks, disks) = q_src;

	submit->cb_fn = cb_fn_orig;
	submit->cb_param = cb_param_orig;
	submit->flags = flags_orig;
	async_tx_sync_epilog(submit);

	return NULL;
	}
	}
	EXPORT_SYMBOL_GPL(async_syndrome_val);

	static int __init async_pq_init(void)
	{
	scribble = alloc_page(GFP_KERNEL);

	if (scribble)
	return 0;

	pr_err("%s: failed to allocate required spare page\n", __func__);

	return -ENOMEM;
	}

	static void __exit async_pq_exit(void)
	{
	put_page(scribble);
	}

	module_init(async_pq_init);
	module_exit(async_pq_exit);

	MODULE_DESCRIPTION("asynchronous raid6 syndrome generation/validation");
	MODULE_LICENSE("GPL");