This is a note to let you know that I've just added the patch titled
dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dmaengine-stm32-dma-avoid-64-bit-division-in-stm32_d.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4577086ed03ca96e71303a2a745527124b2e1a7e
Author: Arnd Bergmann <arnd@xxxxxxxx>
Date: Wed Nov 3 16:33:12 2021 +0100
dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width
[ Upstream commit 2498363310e9b5e5de0e104709adc35c9f3ff7d9 ]
Using the % operator on a 64-bit variable is expensive and can
cause a link failure:
arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_get_max_width':
stm32-dma.c:(.text+0x170): undefined reference to `__aeabi_uldivmod'
arm-linux-gnueabi-ld: drivers/dma/stm32-dma.o: in function `stm32_dma_set_xfer_param':
stm32-dma.c:(.text+0x1cd4): undefined reference to `__aeabi_uldivmod'
As we know that we just want to check the alignment in
stm32_dma_get_max_width(), there is no need for a full division, and
using a simple mask is a faster replacement.
Same in stm32_dma_set_xfer_param(), change this to only allow burst
transfers if the address is a multiple of the length.
stm32_dma_get_best_burst just after will take buf_len into account to fix
burst in case of misalignment.
Fixes: b20fd5fa310c ("dmaengine: stm32-dma: fix stm32_dma_get_max_width")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20211103153312.41483-1-amelie.delaunay@xxxxxxxxxxx
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index c276a39aa7930..7dfc743ac4338 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -280,7 +280,7 @@ static enum dma_slave_buswidth stm32_dma_get_max_width(u32 buf_len,
max_width > DMA_SLAVE_BUSWIDTH_1_BYTE)
max_width = max_width >> 1;
- if (buf_addr % max_width)
+ if (buf_addr & (max_width - 1))
max_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
return max_width;
@@ -756,7 +756,7 @@ static int stm32_dma_set_xfer_param(struct stm32_dma_chan *chan,
* Set memory burst size - burst not possible if address is not aligned on
* the address boundary equal to the size of the transfer
*/
- if (buf_addr % buf_len)
+ if (buf_addr & (buf_len - 1))
src_maxburst = 1;
else
src_maxburst = STM32_DMA_MAX_BURST;
@@ -812,7 +812,7 @@ static int stm32_dma_set_xfer_param(struct stm32_dma_chan *chan,
* Set memory burst size - burst not possible if address is not aligned on
* the address boundary equal to the size of the transfer
*/
- if (buf_addr % buf_len)
+ if (buf_addr & (buf_len - 1))
dst_maxburst = 1;
else
dst_maxburst = STM32_DMA_MAX_BURST;
