[PATCH] scatterlist: enable sg chaining for all architectures

From: Akinobu Mita
Date: Sat Apr 25 2015 - 10:57:44 EST

Some architectures enable sg chaining option while others do not.

The requirement to enable sg chaining is that pages must be aligned
at a 32-bit boundary in order to overload the LSB of the pointer.
Regardless of whether ARCH_HAS_SG_CHAIN is defined or not, the above
requirement is always chacked by BUG_ON() in sg_assign_page. So
all architectures can enable sg chaining.

As you can see from the changes in drivers/target/target_core_rd.c,
enabling SG chaining for all architectures allows us to allocate
discontiguous scatterlist tables which can be traversed throughout
by sg_next() without a special handling for some architectures.

Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: "James E.J. Bottomley" <JBottomley@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx
Cc: Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx>
Cc: target-devel@xxxxxxxxxxxxxxx
---
arch/arm/Kconfig | 6 ------
arch/arm64/Kconfig | 1 -
arch/ia64/Kconfig | 1 -
arch/powerpc/Kconfig | 1 -
arch/s390/Kconfig | 1 -
arch/sparc/Kconfig | 1 -
arch/x86/Kconfig | 1 -
drivers/target/target_core_rd.c | 45 -----------------------------------------
include/linux/scatterlist.h | 4 ----
include/scsi/scsi.h | 8 ++------
lib/Kconfig | 7 -------
lib/scatterlist.c | 8 --------
12 files changed, 2 insertions(+), 82 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 45df48b..4436000 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -89,16 +89,11 @@ config ARM
Europe. There is an ARM Linux project with a web page at
<http://www.arm.linux.org.uk/>.

-config ARM_HAS_SG_CHAIN
- select ARCH_HAS_SG_CHAIN
- bool
-
config NEED_SG_DMA_LENGTH
bool

config ARM_DMA_USE_IOMMU
bool
- select ARM_HAS_SG_CHAIN
select NEED_SG_DMA_LENGTH

if ARM_DMA_USE_IOMMU
@@ -318,7 +313,6 @@ config ARCH_MULTIPLATFORM
bool "Allow multiple platforms to be selected"
depends on MMU
select ARCH_WANT_OPTIONAL_GPIOLIB
- select ARM_HAS_SG_CHAIN
select ARM_PATCH_PHYS_VIRT
select AUTO_ZRELADDR
select CLKSRC_OF
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 4269dba..582462a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -5,7 +5,6 @@ config ARM64
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_GCOV_PROFILE_ALL
- select ARCH_HAS_SG_CHAIN
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_SUPPORTS_ATOMIC_RMW
diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 76d25b2..a9f896e 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -32,7 +32,6 @@ config IA64
select HAVE_MEMBLOCK
select HAVE_MEMBLOCK_NODE_MAP
select HAVE_VIRT_CPU_ACCOUNTING
- select ARCH_HAS_SG_CHAIN
select VIRT_TO_BUS
select ARCH_DISCARD_MEMBLOCK
select GENERIC_IRQ_PROBE
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 190cc48..6f3b6768 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -112,7 +112,6 @@ config PPC
select HAVE_DMA_API_DEBUG
select HAVE_OPROFILE
select HAVE_DEBUG_KMEMLEAK
- select ARCH_HAS_SG_CHAIN
select GENERIC_ATOMIC64 if PPC32
select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
select HAVE_PERF_EVENTS
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 8e58c61..2854e52 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -67,7 +67,6 @@ config S390
select ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_GCOV_PROFILE_ALL
- select ARCH_HAS_SG_CHAIN
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_INLINE_READ_LOCK
select ARCH_INLINE_READ_LOCK_BH
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index e49502a..d0512f5 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -42,7 +42,6 @@ config SPARC
select MODULES_USE_ELF_RELA
select ODD_RT_SIGACTION
select OLD_SIGSUSPEND
- select ARCH_HAS_SG_CHAIN

config SPARC32
def_bool !64BIT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 226d569..eeb52b8 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -101,7 +101,6 @@ config X86
select HAVE_BPF_JIT if X86_64
select HAVE_ARCH_TRANSPARENT_HUGEPAGE
select HAVE_ARCH_HUGE_VMAP if X86_64 || (X86_32 && X86_PAE)
- select ARCH_HAS_SG_CHAIN
select CLKEVT_I8253
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select GENERIC_IOMAP
diff --git a/drivers/target/target_core_rd.c b/drivers/target/target_core_rd.c
index fa20d67..ce6a0ac 100644
--- a/drivers/target/target_core_rd.c
+++ b/drivers/target/target_core_rd.c
@@ -144,16 +144,12 @@ static int rd_allocate_sgl_table(struct rd_dev *rd_dev, struct rd_dev_sg_table *
sg_per_table = (total_sg_needed > max_sg_per_table) ?
max_sg_per_table : total_sg_needed;

-#ifdef CONFIG_ARCH_HAS_SG_CHAIN
-
/*
* Reserve extra element for chain entry
*/
if (sg_per_table < total_sg_needed)
chain_entry = 1;

-#endif /* CONFIG_ARCH_HAS_SG_CHAIN */
-
sg = kcalloc(sg_per_table + chain_entry, sizeof(*sg),
GFP_KERNEL);
if (!sg) {
@@ -164,15 +160,11 @@ static int rd_allocate_sgl_table(struct rd_dev *rd_dev, struct rd_dev_sg_table *

sg_init_table(sg, sg_per_table + chain_entry);

-#ifdef CONFIG_ARCH_HAS_SG_CHAIN
-
if (i > 0) {
sg_chain(sg_table[i - 1].sg_table,
max_sg_per_table + 1, sg);
}

-#endif /* CONFIG_ARCH_HAS_SG_CHAIN */
-
sg_table[i].sg_table = sg;
sg_table[i].rd_sg_count = sg_per_table;
sg_table[i].page_start_offset = page_offset;
@@ -420,7 +412,6 @@ static sense_reason_t rd_do_prot_rw(struct se_cmd *cmd, dif_verify dif_verify)
struct scatterlist *prot_sg;
u32 sectors = cmd->data_length / se_dev->dev_attrib.block_size;
u32 prot_offset, prot_page;
- u32 prot_npages __maybe_unused;
u64 tmp;
sense_reason_t rc = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;

@@ -435,42 +426,6 @@ static sense_reason_t rd_do_prot_rw(struct se_cmd *cmd, dif_verify dif_verify)
prot_sg = &prot_table->sg_table[prot_page -
prot_table->page_start_offset];

-#ifndef CONFIG_ARCH_HAS_SG_CHAIN
-
- prot_npages = DIV_ROUND_UP(prot_offset + sectors * se_dev->prot_length,
- PAGE_SIZE);
-
- /*
- * Allocate temporaly contiguous scatterlist entries if prot pages
- * straddles multiple scatterlist tables.
- */
- if (prot_table->page_end_offset < prot_page + prot_npages - 1) {
- int i;
-
- prot_sg = kcalloc(prot_npages, sizeof(*prot_sg), GFP_KERNEL);
- if (!prot_sg)
- return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
-
- need_to_release = true;
- sg_init_table(prot_sg, prot_npages);
-
- for (i = 0; i < prot_npages; i++) {
- if (prot_page + i > prot_table->page_end_offset) {
- prot_table = rd_get_prot_table(dev,
- prot_page + i);
- if (!prot_table) {
- kfree(prot_sg);
- return rc;
- }
- sg_unmark_end(&prot_sg[i - 1]);
- }
- prot_sg[i] = prot_table->sg_table[prot_page + i -
- prot_table->page_start_offset];
- }
- }
-
-#endif /* !CONFIG_ARCH_HAS_SG_CHAIN */
-
rc = dif_verify(cmd, cmd->t_task_lba, sectors, 0, prot_sg, prot_offset);
if (need_to_release)
kfree(prot_sg);
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index ed8f9e7..bee59ea 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -136,10 +136,6 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
struct scatterlist *sgl)
{
-#ifndef CONFIG_ARCH_HAS_SG_CHAIN
- BUG();
-#endif
-
/*
* offset and length are unused for chain entry. Clear them.
*/
diff --git a/include/scsi/scsi.h b/include/scsi/scsi.h
index d0a66aa..f01c5bb 100644
--- a/include/scsi/scsi.h
+++ b/include/scsi/scsi.h
@@ -28,14 +28,10 @@ enum scsi_timeouts {
#define SCSI_MAX_SG_SEGMENTS 128

/*
- * Like SCSI_MAX_SG_SEGMENTS, but for archs that have sg chaining. This limit
- * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
+ * This limit is totally arbitrary, a setting of 2048 will get you at least
+ * 8mb ios.
*/
-#ifdef CONFIG_ARCH_HAS_SG_CHAIN
#define SCSI_MAX_SG_CHAIN_SEGMENTS 2048
-#else
-#define SCSI_MAX_SG_CHAIN_SEGMENTS SCSI_MAX_SG_SEGMENTS
-#endif

/*
* DIX-capable adapters effectively support infinite chaining for the
diff --git a/lib/Kconfig b/lib/Kconfig
index 601965a..0b938d2 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -515,11 +515,4 @@ config UCS2_STRING

source "lib/fonts/Kconfig"

-#
-# sg chaining option
-#
-
-config ARCH_HAS_SG_CHAIN
- def_bool n
-
endmenu
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index c9f2e8c..6d9d477 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -73,16 +73,12 @@ EXPORT_SYMBOL(sg_nents);
**/
struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
{
-#ifndef CONFIG_ARCH_HAS_SG_CHAIN
- struct scatterlist *ret = &sgl[nents - 1];
-#else
struct scatterlist *sg, *ret = NULL;
unsigned int i;

for_each_sg(sgl, sg, nents, i)
ret = sg;

-#endif
#ifdef CONFIG_DEBUG_SG
BUG_ON(sgl[0].sg_magic != SG_MAGIC);
BUG_ON(!sg_is_last(ret));
@@ -255,10 +251,6 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,

if (nents == 0)
return -EINVAL;
-#ifndef CONFIG_ARCH_HAS_SG_CHAIN
- if (WARN_ON_ONCE(nents > max_ents))
- return -EINVAL;
-#endif

left = nents;
prv = NULL;
--
1.9.1

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