2021-11-03 15:36:19

by Amelie Delaunay

Subject: [PATCH 1/1] dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width

From: Arnd Bergmann <[email protected]>

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 <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Amelie Delaunay <[email protected]>
---
drivers/dma/stm32-dma.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 2283c500f4ce..83a37a6955a3 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;
@@ -757,7 +757,7 @@ 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;
@@ -813,7 +813,7 @@ 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;
--
2.25.1

2021-11-09 14:21:57

by Vinod Koul

Subject: Re: [PATCH 1/1] dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width

On 03-11-21, 16:33, Amelie Delaunay wrote:
> From: Arnd Bergmann <[email protected]>
>
> 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.

Applied, thanks

--
~Vinod