Re: [PATCH v3 06/11] scatterlist: support "page-less" (__pfn_t only) entries

From: Williams, Dan J
Date: Wed May 13 2015 - 14:36:07 EST

[ adding willy (yes, need to fix my scripts), and dmaengine folks]

Jens, Christoph,

I've rebased this patch series block/for-next. With commit 84be456f883c
"remove <asm/scatterlist.h>" I think we can take the next step of
removing all references to page_link and just use __pfn_t by default.
v4 patch below.

Jens, I'm wondering if you want to take this series(.) as patches or
prepare a git branch to pull?

8<--------
Subject: scatterlist: support "page-less" (__pfn_t only) entries

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() or sg_last() entry" flags to the new 'flags' field.

[djbw: rebase on block/for-4.2]
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
---
block/blk-merge.c | 2 -
drivers/crypto/omap-sham.c | 2 -
drivers/dma/imx-dma.c | 7 +--
drivers/dma/ste_dma40.c | 5 --
drivers/mmc/card/queue.c | 4 +-
include/crypto/scatterwalk.h | 9 +---
include/linux/scatterlist.h | 92 ++++++++++++++++++++++++++----------------
samples/kfifo/dma-example.c | 8 ++--
8 files changed, 69 insertions(+), 60 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/crypto/omap-sham.c b/drivers/crypto/omap-sham.c
index 4d63e0d4da9a..21736afd3320 100644
--- a/drivers/crypto/omap-sham.c
+++ b/drivers/crypto/omap-sham.c
@@ -582,7 +582,7 @@ static int omap_sham_xmit_dma(struct omap_sham_dev *dd, dma_addr_t dma_addr,
* the dmaengine may try to DMA the incorrect amount of data.
*/
sg_init_table(&ctx->sgl, 1);
- ctx->sgl.page_link = ctx->sg->page_link;
+ ctx->sgl.pfn = ctx->sg->pfn;
ctx->sgl.offset = ctx->sg->offset;
sg_dma_len(&ctx->sgl) = len32;
sg_dma_address(&ctx->sgl) = sg_dma_address(ctx->sg);
diff --git a/drivers/dma/imx-dma.c b/drivers/dma/imx-dma.c
index eed405976ea9..a767727bcfef 100644
--- a/drivers/dma/imx-dma.c
+++ b/drivers/dma/imx-dma.c
@@ -886,7 +886,7 @@ static struct dma_async_tx_descriptor *imxdma_prep_dma_cyclic(
sg_init_table(imxdmac->sg_list, periods);

for (i = 0; i < periods; i++) {
- imxdmac->sg_list[i].page_link = 0;
+ imxdmac->sg_list[i].pfn.page = NULL;
imxdmac->sg_list[i].offset = 0;
imxdmac->sg_list[i].dma_address = dma_addr;
sg_dma_len(&imxdmac->sg_list[i]) = period_len;
@@ -894,10 +894,7 @@ static struct dma_async_tx_descriptor *imxdma_prep_dma_cyclic(
}

/* close the loop */
- imxdmac->sg_list[periods].offset = 0;
- sg_dma_len(&imxdmac->sg_list[periods]) = 0;
- imxdmac->sg_list[periods].page_link =
- ((unsigned long)imxdmac->sg_list | 0x01) & ~0x02;
+ sg_chain(imxdmac->sg_list, periods + 1, imxdmac->sg_list);

desc->type = IMXDMA_DESC_CYCLIC;
desc->sg = imxdmac->sg_list;
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/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index 20e4226a2e14..4529889b0f07 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -25,13 +25,8 @@
#include <linux/scatterlist.h>
#include <linux/sched.h>

-static inline void scatterwalk_sg_chain(struct scatterlist *sg1, int num,
- struct scatterlist *sg2)
-{
- sg_set_page(&sg1[num - 1], (void *)sg2, 0, 0);
- sg1[num - 1].page_link &= ~0x02;
- sg1[num - 1].page_link |= 0x01;
-}
+#define scatterwalk_sg_chain(prv, num, sgl) sg_chain(prv, num, sgl)
+#define scatterwalk_sg_next(sgl) sg_next(sgl)

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 eca1ec93775c..98c21b460292 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -9,14 +9,18 @@

struct scatterlist {
#ifdef CONFIG_DEBUG_SG
- unsigned long sg_magic;
+ unsigned long sg_magic;
#endif
- unsigned long page_link;
- unsigned int offset;
- unsigned int length;
- dma_addr_t dma_address;
+ union {
+ __pfn_t pfn;
+ struct scatterlist *next;
+ };
+ unsigned short offset;
+ unsigned short sg_flags;
+ unsigned int length;
+ dma_addr_t dma_address;
#ifdef CONFIG_NEED_SG_DMA_LENGTH
- unsigned int dma_length;
+ unsigned int dma_length;
#endif
};

@@ -44,30 +48,29 @@ struct sg_table {
/*
* Notes on SG table design.
*
- * We use the unsigned long page_link field in the scatterlist struct to place
- * the page pointer AND encode information about the sg table as well. The two
- * lower bits are reserved for this information.
+ * We use the fact that a given sg entry will never be larger than a
+ * page to pack 'offset' and 'sg_flags' into 32-bits. This supports a
+ * PAGE_SIZE up to 64K and flags to encode information about the sg
+ * entry.
*
- * If bit 0 is set, then the page_link contains a pointer to the next sg
- * table list. Otherwise the next entry is at sg + 1.
+ * If SG_FLAGS_CHAIN is set, then the 'next' member of the entry is a
+ * pointer to the next sg table list. Otherwise the next entry is at sg
+ * + 1.
*
- * If bit 1 is set, then this sg entry is the last element in a list.
+ * If SG_FLAGS_LAST is set, then this sg entry is the last element in a
+ * list.
*
* See sg_next().
*
*/

#define SG_MAGIC 0x87654321
+#define SG_FLAGS_CHAIN 0x0001
+#define SG_FLAGS_LAST 0x0002

-/*
- * 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_chain_ptr(sg) \
- ((struct scatterlist *) ((sg)->page_link & ~0x03))
+#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)

/**
* sg_assign_page - Assign a given page to an SG entry
@@ -81,18 +84,15 @@ struct sg_table {
**/
static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
{
- unsigned long page_link = sg->page_link & 0x3;
-
- /*
- * In order for the low bit stealing approach to work, pages
- * must be aligned at a 32-bit boundary as a minimum.
- */
- BUG_ON((unsigned long) page & 0x03);
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
- sg->page_link = page_link | (unsigned long) page;
+ sg->pfn = page_to_pfn_t(page);
+#ifdef CONFIG_DEBUG_SG
+ BUG_ON(sg->sg_magic != SG_MAGIC);
+ BUG_ON(sg_is_chain(sg));
+#endif
}

/**
@@ -113,17 +113,32 @@ 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;
}

+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;
+}
+
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
- return (struct page *)((sg)->page_link & ~0x3);
+ return __pfn_t_to_page(sg->pfn);
}

/**
@@ -175,7 +190,8 @@ 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.
*/
- prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
+ prv[prv_nents - 1].next = sgl;
+ prv[prv_nents - 1].sg_flags = SG_FLAGS_CHAIN;
}

/**
@@ -195,8 +211,8 @@ static inline void sg_mark_end(struct scatterlist *sg)
/*
* Set termination bit, clear potential chain bit
*/
- sg->page_link |= 0x02;
- sg->page_link &= ~0x01;
+ sg->sg_flags |= SG_FLAGS_LAST;
+ sg->sg_flags &= ~SG_FLAGS_CHAIN;
}

/**
@@ -212,7 +228,7 @@ 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;
+ sg->sg_flags &= ~SG_FLAGS_LAST;
}

/**
@@ -227,7 +243,7 @@ static inline void sg_unmark_end(struct scatterlist *sg)
**/
static inline dma_addr_t sg_phys(struct scatterlist *sg)
{
- return page_to_phys(sg_page(sg)) + sg->offset;
+ return __pfn_t_to_phys(sg->pfn) + sg->offset;
}

/**
@@ -242,7 +258,11 @@ 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;
+
+ page = __pfn_t_to_page(sg->pfn) + sg->offset;
+ BUG_ON(!page); /* don't use sg_virt() on unmapped memory */
+ return page_address(page) + sg->offset;
}

int sg_nents(struct scatterlist *sg);
diff --git a/samples/kfifo/dma-example.c b/samples/kfifo/dma-example.c
index aa243db93f01..3eeff9a56e0e 100644
--- a/samples/kfifo/dma-example.c
+++ b/samples/kfifo/dma-example.c
@@ -75,8 +75,8 @@ static int __init example_init(void)
for (i = 0; i < nents; i++) {
printk(KERN_INFO
"sg[%d] -> "
- "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
- i, sg[i].page_link, sg[i].offset, sg[i].length);
+ "pfn_data 0x%.8lx offset 0x%.8x length 0x%.8x\n",
+ i, sg[i].pfn.data, sg[i].offset, sg[i].length);

if (sg_is_last(&sg[i]))
break;
@@ -104,8 +104,8 @@ static int __init example_init(void)
for (i = 0; i < nents; i++) {
printk(KERN_INFO
"sg[%d] -> "
- "page_link 0x%.8lx offset 0x%.8x length 0x%.8x\n",
- i, sg[i].page_link, sg[i].offset, sg[i].length);
+ "pfn_data 0x%.8lx offset 0x%.8x length 0x%.8x\n",
+ i, sg[i].pfn.data, sg[i].offset, sg[i].length);

if (sg_is_last(&sg[i]))
break;

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