[PATCH] swiotlb: set IO TLB segment size via cmdline

Roman Skakun
2021-09-14T15:10:43Z

From: Roman Skakun <roman_skakun@epam.com>

It is possible when default IO TLB size is not
enough to fit a long buffers as described here [1].

This patch makes a way to set this parameter
using cmdline instead of recompiling a kernel.

[1] https://www.xilinx.com/support/answers/72694.html

Signed-off-by: Roman Skakun <roman_skakun@epam.com>
---
.../admin-guide/kernel-parameters.txt | 5 +-
arch/mips/cavium-octeon/dma-octeon.c | 2 +-
arch/powerpc/platforms/pseries/svm.c | 2 +-
drivers/xen/swiotlb-xen.c | 7 +--
include/linux/swiotlb.h | 1 +
kernel/dma/swiotlb.c | 51 ++++++++++++++-----
6 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..f842a523a485 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5558,8 +5558,9 @@
it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)

swiotlb= [ARM,IA-64,PPC,MIPS,X86]
- Format: { <int> | force | noforce }
- <int> -- Number of I/O TLB slabs
+ Format: { <slabs> [,<io_tlb_segment_size>] [,force | noforce]​ }
+ <slabs> -- Number of I/O TLB slabs
+ <io_tlb_segment_size> -- Max IO TLB segment size
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
noforce -- Never use bounce buffers (for debugging)
diff --git a/arch/mips/cavium-octeon/dma-octeon.c b/arch/mips/cavium-octeon/dma-octeon.c
index df70308db0e6..446c73bc936e 100644
--- a/arch/mips/cavium-octeon/dma-octeon.c
+++ b/arch/mips/cavium-octeon/dma-octeon.c
@@ -237,7 +237,7 @@ void __init plat_swiotlb_setup(void)
swiotlbsize = 64 * (1<<20);
#endif
swiotlb_nslabs = swiotlbsize >> IO_TLB_SHIFT;
- swiotlb_nslabs = ALIGN(swiotlb_nslabs, IO_TLB_SEGSIZE);
+ swiotlb_nslabs = ALIGN(swiotlb_nslabs, swiotlb_io_seg_size());
swiotlbsize = swiotlb_nslabs << IO_TLB_SHIFT;

octeon_swiotlb = memblock_alloc_low(swiotlbsize, PAGE_SIZE);
diff --git a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platforms/pseries/svm.c
index 87f001b4c4e4..2a1f09c722ac 100644
--- a/arch/powerpc/platforms/pseries/svm.c
+++ b/arch/powerpc/platforms/pseries/svm.c
@@ -47,7 +47,7 @@ void __init svm_swiotlb_init(void)
unsigned long bytes, io_tlb_nslabs;

io_tlb_nslabs = (swiotlb_size_or_default() >> IO_TLB_SHIFT);
- io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
+ io_tlb_nslabs = ALIGN(io_tlb_nslabs, swiotlb_io_seg_size());

bytes = io_tlb_nslabs << IO_TLB_SHIFT;

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 643fe440c46e..0fc9c6cb6815 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -110,12 +110,13 @@ static int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
int dma_bits;
dma_addr_t dma_handle;
phys_addr_t p = virt_to_phys(buf);
+ unsigned long tlb_segment_size = swiotlb_io_seg_size();

- dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;
+ dma_bits = get_order(tlb_segment_size << IO_TLB_SHIFT) + PAGE_SHIFT;

i = 0;
do {
- int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);
+ int slabs = min(nslabs - i, (unsigned long)tlb_segment_size);

do {
rc = xen_create_contiguous_region(
@@ -153,7 +154,7 @@ static const char *xen_swiotlb_error(enum xen_swiotlb_err err)
return "";
}

-#define DEFAULT_NSLABS ALIGN(SZ_64M >> IO_TLB_SHIFT, IO_TLB_SEGSIZE)
+#define DEFAULT_NSLABS ALIGN(SZ_64M >> IO_TLB_SHIFT, swiotlb_io_seg_size())

int __ref xen_swiotlb_init(void)
{
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index b0cb2a9973f4..35c3ffeda9fa 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -59,6 +59,7 @@ void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,
size_t size, enum dma_data_direction dir);
dma_addr_t swiotlb_map(struct device *dev, phys_addr_t phys,
size_t size, enum dma_data_direction dir, unsigned long attrs);
+unsigned long swiotlb_io_seg_size(void);

#ifdef CONFIG_SWIOTLB
extern enum swiotlb_force swiotlb_force;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 87c40517e822..6b505206fc13 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -72,6 +72,11 @@ enum swiotlb_force swiotlb_force;

struct io_tlb_mem io_tlb_default_mem;

+/*
+ * Maximum IO TLB segment size.
+ */
+static unsigned long io_tlb_seg_size = IO_TLB_SEGSIZE;
+
/*
* Max segment that we can provide which (if pages are contingous) will
* not be bounced (unless SWIOTLB_FORCE is set).
@@ -81,15 +86,30 @@ static unsigned int max_segment;
static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;

static int __init
-setup_io_tlb_npages(char *str)
+setup_io_tlb_params(char *str)
{
+ unsigned long tmp;
+
if (isdigit(*str)) {
- /* avoid tail segment of size < IO_TLB_SEGSIZE */
- default_nslabs =
- ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
+ default_nslabs = simple_strtoul(str, &str, 0);
}
if (*str == ',')
++str;
+
+ /* get max IO TLB segment size */
+ if (isdigit(*str)) {
+ tmp = simple_strtoul(str, &str, 0);
+ if (tmp)
+ io_tlb_seg_size = ALIGN(tmp, IO_TLB_SEGSIZE);
+ }
+ if (*str == ',')
+ ++str;
+
+ /* update io_tlb_nslabs after applying a new segment size and
+ * avoid tail segment of size < IO TLB segment size
+ */
+ default_nslabs = ALIGN(default_nslabs, io_tlb_seg_size);
+
if (!strcmp(str, "force"))
swiotlb_force = SWIOTLB_FORCE;
else if (!strcmp(str, "noforce"))
@@ -97,7 +117,7 @@ setup_io_tlb_npages(char *str)

return 0;
}
-early_param("swiotlb", setup_io_tlb_npages);
+early_param("swiotlb", setup_io_tlb_params);

unsigned int swiotlb_max_segment(void)
{
@@ -118,6 +138,11 @@ unsigned long swiotlb_size_or_default(void)
return default_nslabs << IO_TLB_SHIFT;
}

+unsigned long swiotlb_io_seg_size(void)
+{
+ return io_tlb_seg_size;
+}
+
void __init swiotlb_adjust_size(unsigned long size)
{
/*
@@ -128,7 +153,7 @@ void __init swiotlb_adjust_size(unsigned long size)
if (default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT)
return;
size = ALIGN(size, IO_TLB_SIZE);
- default_nslabs = ALIGN(size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
+ default_nslabs = ALIGN(size >> IO_TLB_SHIFT, io_tlb_seg_size);
pr_info("SWIOTLB bounce buffer size adjusted to %luMB", size >> 20);
}

@@ -147,7 +172,7 @@ void swiotlb_print_info(void)

static inline unsigned long io_tlb_offset(unsigned long val)
{
- return val & (IO_TLB_SEGSIZE - 1);
+ return val & (io_tlb_seg_size - 1);
}

static inline unsigned long nr_slots(u64 val)
@@ -192,7 +217,7 @@ static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,

spin_lock_init(&mem->lock);
for (i = 0; i < mem->nslabs; i++) {
- mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
+ mem->slots[i].list = io_tlb_seg_size - io_tlb_offset(i);
mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
mem->slots[i].alloc_size = 0;
}
@@ -261,7 +286,7 @@ int
swiotlb_late_init_with_default_size(size_t default_size)
{
unsigned long nslabs =
- ALIGN(default_size >> IO_TLB_SHIFT, IO_TLB_SEGSIZE);
+ ALIGN(default_size >> IO_TLB_SHIFT, io_tlb_seg_size);
unsigned long bytes;
unsigned char *vstart = NULL;
unsigned int order;
@@ -522,7 +547,7 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
alloc_size - (offset + ((i - index) << IO_TLB_SHIFT));
}
for (i = index - 1;
- io_tlb_offset(i) != IO_TLB_SEGSIZE - 1 &&
+ io_tlb_offset(i) != io_tlb_seg_size - 1 &&
mem->slots[i].list; i--)
mem->slots[i].list = ++count;

@@ -600,7 +625,7 @@ static void swiotlb_release_slots(struct device *dev, phys_addr_t tlb_addr)
* with slots below and above the pool being returned.
*/
spin_lock_irqsave(&mem->lock, flags);
- if (index + nslots < ALIGN(index + 1, IO_TLB_SEGSIZE))
+ if (index + nslots < ALIGN(index + 1, io_tlb_seg_size))
count = mem->slots[index + nslots].list;
else
count = 0;
@@ -620,7 +645,7 @@ static void swiotlb_release_slots(struct device *dev, phys_addr_t tlb_addr)
* available (non zero)
*/
for (i = index - 1;
- io_tlb_offset(i) != IO_TLB_SEGSIZE - 1 && mem->slots[i].list;
+ io_tlb_offset(i) != io_tlb_seg_size - 1 && mem->slots[i].list;
i--)
mem->slots[i].list = ++count;
mem->used -= nslots;
@@ -698,7 +723,7 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,

size_t swiotlb_max_mapping_size(struct device *dev)
{
- return ((size_t)IO_TLB_SIZE) * IO_TLB_SEGSIZE;
+ return ((size_t)IO_TLB_SIZE) * io_tlb_seg_size;
}

bool is_swiotlb_active(struct device *dev)
--
2.27.0