[PATCH v2 06/10] scatterlist: support "page-less" (__pfn_t only) entries

From: Dan Williams
Date: Wed May 06 2015 - 16:08:21 EST

From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>

Given that an offset will never be more than PAGE_SIZE, steal the unused
bits of the offset to implement a flags field. Move the existing "this
is a sg_chain() entry" flag to the new flags field, and add a new flag
(SG_FLAGS_PAGE) to indicate that there is a struct page backing for the
entry.

Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
---
block/blk-merge.c | 2 -
drivers/dma/ste_dma40.c | 5 --
drivers/mmc/card/queue.c | 4 +-
include/asm-generic/scatterlist.h | 9 ++++
include/crypto/scatterwalk.h | 10 ++++
include/linux/scatterlist.h | 91 +++++++++++++++++++++++++++++++++----
6 files changed, 105 insertions(+), 16 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 218ad1e57a49..82a688551b72 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -267,7 +267,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
if (rq->cmd_flags & REQ_WRITE)
memset(q->dma_drain_buffer, 0, q->dma_drain_size);

- sg->page_link &= ~0x02;
+ sg_unmark_end(sg);
sg = sg_next(sg);
sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
q->dma_drain_size,
diff --git a/drivers/dma/ste_dma40.c b/drivers/dma/ste_dma40.c
index 3c10f034d4b9..e8c00642cacb 100644
--- a/drivers/dma/ste_dma40.c
+++ b/drivers/dma/ste_dma40.c
@@ -2562,10 +2562,7 @@ dma40_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t dma_addr,
dma_addr += period_len;
}

- sg[periods].offset = 0;
- sg_dma_len(&sg[periods]) = 0;
- sg[periods].page_link =
- ((unsigned long)sg | 0x01) & ~0x02;
+ sg_chain(sg, periods + 1, sg);

txd = d40_prep_sg(chan, sg, sg, periods, direction,
DMA_PREP_INTERRUPT);
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 236d194c2883..127f76294e71 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -469,7 +469,7 @@ static unsigned int mmc_queue_packed_map_sg(struct mmc_queue *mq,
sg_set_buf(__sg, buf + offset, len);
offset += len;
remain -= len;
- (__sg++)->page_link &= ~0x02;
+ sg_unmark_end(__sg++);
sg_len++;
} while (remain);
}
@@ -477,7 +477,7 @@ static unsigned int mmc_queue_packed_map_sg(struct mmc_queue *mq,
list_for_each_entry(req, &packed->list, queuelist) {
sg_len += blk_rq_map_sg(mq->queue, req, __sg);
__sg = sg + (sg_len - 1);
- (__sg++)->page_link &= ~0x02;
+ sg_unmark_end(__sg++);
}
sg_mark_end(sg + (sg_len - 1));
return sg_len;
diff --git a/include/asm-generic/scatterlist.h b/include/asm-generic/scatterlist.h
index 5de07355fad4..959f51572a8e 100644
--- a/include/asm-generic/scatterlist.h
+++ b/include/asm-generic/scatterlist.h
@@ -7,8 +7,17 @@ struct scatterlist {
#ifdef CONFIG_DEBUG_SG
unsigned long sg_magic;
#endif
+#ifdef CONFIG_HAVE_DMA_PFN
+ union {
+ __pfn_t pfn;
+ struct scatterlist *next;
+ };
+ unsigned short offset;
+ unsigned short sg_flags;
+#else
unsigned long page_link;
unsigned int offset;
+#endif
unsigned int length;
dma_addr_t dma_address;
#ifdef CONFIG_NEED_SG_DMA_LENGTH
diff --git a/include/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index 20e4226a2e14..7296d89a50b2 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -25,6 +25,15 @@
#include <linux/scatterlist.h>
#include <linux/sched.h>

+#ifdef CONFIG_HAVE_DMA_PFN
+/*
+ * If we're using PFNs, the architecture must also have been converted to
+ * support SG_CHAIN. So we can use the generic code instead of custom
+ * code.
+ */
+#define scatterwalk_sg_chain(prv, num, sgl) sg_chain(prv, num, sgl)
+#define scatterwalk_sg_next(sgl) sg_next(sgl)
+#else
static inline void scatterwalk_sg_chain(struct scatterlist *sg1, int num,
struct scatterlist *sg2)
{
@@ -32,6 +41,7 @@ static inline void scatterwalk_sg_chain(struct scatterlist *sg1, int num,
sg1[num - 1].page_link &= ~0x02;
sg1[num - 1].page_link |= 0x01;
}
+#endif

static inline void scatterwalk_crypto_chain(struct scatterlist *head,
struct scatterlist *sg,
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index ed8f9e70df9b..9d423e559bdb 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -5,6 +5,7 @@
#include <linux/bug.h>
#include <linux/mm.h>

+#include <asm/page.h>
#include <asm/types.h>
#include <asm/scatterlist.h>
#include <asm/io.h>
@@ -18,8 +19,14 @@ struct sg_table {
/*
* Notes on SG table design.
*
- * Architectures must provide an unsigned long page_link field in the
- * scatterlist struct. We use that to place the page pointer AND encode
+ * Architectures may define CONFIG_HAVE_DMA_PFN to indicate that they wish
+ * to support SGLs that point to pages which do not have a struct page to
+ * describe them. If so, they should provide an sg_flags field in their
+ * scatterlist struct (see asm-generic for an example) as well as a pfn
+ * field.
+ *
+ * Otherwise, architectures must provide an unsigned long page_link field in
+ * the scatterlist struct. We use that to place the page pointer AND encode
* information about the sg table as well. The two lower bits are reserved
* for this information.
*
@@ -33,16 +40,25 @@ struct sg_table {
*/

#define SG_MAGIC 0x87654321
-
+#define SG_FLAGS_CHAIN 0x0001
+#define SG_FLAGS_LAST 0x0002
+#define SG_FLAGS_PAGE 0x0004
+
+#ifdef CONFIG_HAVE_DMA_PFN
+#define sg_is_chain(sg) ((sg)->sg_flags & SG_FLAGS_CHAIN)
+#define sg_is_last(sg) ((sg)->sg_flags & SG_FLAGS_LAST)
+#define sg_chain_ptr(sg) ((sg)->next)
+#else /* !CONFIG_HAVE_DMA_PFN */
/*
* We overload the LSB of the page pointer to indicate whether it's
* a valid sg entry, or whether it points to the start of a new scatterlist.
* Those low bits are there for everyone! (thanks mason :-)
*/
-#define sg_is_chain(sg) ((sg)->page_link & 0x01)
-#define sg_is_last(sg) ((sg)->page_link & 0x02)
+#define sg_is_chain(sg) ((sg)->page_link & SG_FLAGS_CHAIN)
+#define sg_is_last(sg) ((sg)->page_link & SG_FLAGS_LAST)
#define sg_chain_ptr(sg) \
((struct scatterlist *) ((sg)->page_link & ~0x03))
+#endif /* !CONFIG_HAVE_DMA_PFN */

/**
* sg_assign_page - Assign a given page to an SG entry
@@ -56,6 +72,14 @@ struct sg_table {
**/
static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
{
+#ifdef CONFIG_HAVE_DMA_PFN
+#ifdef CONFIG_DEBUG_SG
+ BUG_ON(sg->sg_magic != SG_MAGIC);
+ BUG_ON(sg_is_chain(sg));
+#endif
+ sg->pfn = page_to_pfn_t(page);
+ sg->sg_flags |= SG_FLAGS_PAGE;
+#else /* !CONFIG_HAVE_DMA_PFN */
unsigned long page_link = sg->page_link & 0x3;

/*
@@ -68,6 +92,7 @@ static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
BUG_ON(sg_is_chain(sg));
#endif
sg->page_link = page_link | (unsigned long) page;
+#endif /* !CONFIG_HAVE_DMA_PFN */
}

/**
@@ -88,17 +113,39 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
unsigned int len, unsigned int offset)
{
sg_assign_page(sg, page);
+ BUG_ON(offset > 65535);
sg->offset = offset;
sg->length = len;
}

+#ifdef CONFIG_HAVE_DMA_PFN
+static inline void sg_set_pfn(struct scatterlist *sg, __pfn_t pfn,
+ unsigned int len, unsigned int offset)
+{
+#ifdef CONFIG_DEBUG_SG
+ BUG_ON(sg->sg_magic != SG_MAGIC);
+ BUG_ON(sg_is_chain(sg));
+#endif
+ sg->pfn = pfn;
+ BUG_ON(offset > 65535);
+ sg->offset = offset;
+ sg->sg_flags = 0;
+ sg->length = len;
+}
+#endif
+
static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
+#ifdef CONFIG_HAVE_DMA_PFN
+ BUG_ON(!(sg->sg_flags & SG_FLAGS_PAGE));
+ return __pfn_t_to_page(sg->pfn);
+#else
return (struct page *)((sg)->page_link & ~0x3);
+#endif
}

/**
@@ -150,7 +197,12 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
* Set lowest bit to indicate a link pointer, and make sure to clear
* the termination bit if it happens to be set.
*/
+#ifdef CONFIG_HAVE_DMA_PFN
+ prv[prv_nents - 1].next = sgl;
+ prv[prv_nents - 1].sg_flags = SG_FLAGS_CHAIN;
+#else
prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
+#endif
}

/**
@@ -170,8 +222,13 @@ static inline void sg_mark_end(struct scatterlist *sg)
/*
* Set termination bit, clear potential chain bit
*/
- sg->page_link |= 0x02;
- sg->page_link &= ~0x01;
+#ifdef CONFIG_HAVE_DMA_PFN
+ sg->sg_flags |= SG_FLAGS_LAST;
+ sg->sg_flags &= ~SG_FLAGS_CHAIN;
+#else
+ sg->page_link |= SG_FLAGS_LAST;
+ sg->page_link &= ~SG_FLAGS_CHAIN;
+#endif
}

/**
@@ -187,7 +244,11 @@ static inline void sg_unmark_end(struct scatterlist *sg)
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
- sg->page_link &= ~0x02;
+#ifdef CONFIG_HAVE_DMA_PFN
+ sg->sg_flags &= ~SG_FLAGS_LAST;
+#else
+ sg->page_link &= ~SG_FLAGS_LAST;
+#endif
}

/**
@@ -202,7 +263,11 @@ static inline void sg_unmark_end(struct scatterlist *sg)
**/
static inline dma_addr_t sg_phys(struct scatterlist *sg)
{
+#ifdef CONFIG_HAVE_DMA_PFN
+ return __pfn_t_to_phys(sg->pfn) + sg->offset;
+#else
return page_to_phys(sg_page(sg)) + sg->offset;
+#endif
}

/**
@@ -217,7 +282,15 @@ static inline dma_addr_t sg_phys(struct scatterlist *sg)
**/
static inline void *sg_virt(struct scatterlist *sg)
{
- return page_address(sg_page(sg)) + sg->offset;
+ struct page *page;
+
+#ifdef CONFIG_HAVE_DMA_PFN
+ page = __pfn_t_to_page(sg->pfn) + sg->offset;
+ BUG_ON(!page); /* don't use sg_virt() on unmapped memory */
+#else
+ page = sg_page(sg);
+#endif
+ return page_address(page) + sg->offset;
}

int sg_nents(struct scatterlist *sg);

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