Hi Arnd,
Thanks for your patch.
On 10/19/21 5:35 PM, Arnd Bergmann wrote:
From: Arnd Bergmann <arnd@xxxxxxxx>
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.
In stm32_dma_set_xfer_param(), it is possible to pass a non-power-of-two
length, so this does not work. I assume this would in fact be a mistake,
and the hardware does not work correctly with a burst of e.g. 5 bytes
on a five-byte aligned address. Change this to only allow burst
transfers if the address is a multiple of the length, and that length
is a power-of-two number.
Fixes: b20fd5fa310c ("dmaengine: stm32-dma: fix stm32_dma_get_max_width")
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
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..102278f7d13e 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 (!is_power_of_2(buf_len) || (buf_addr & (buf_len -1)))
No need to check !is_power_of_2(buf_len) here.
Just after computing src_maxburst,
src_best_burst = stm32_dma_get_best_burst(buf_len,
src_maxburst,
fifoth,
src_addr_width);
The configured burst (src_best_best) already take buf_len into account.
So I would remove !is_power_of_2(buf_len) from the if here and fix the
missing space:
CHECK: spaces preferred around that '-' (ctx:WxV)
#68: FILE: drivers/dma/stm32-dma.c:760:
+ if (!is_power_of_2(buf_len) || (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 (!is_power_of_2(buf_len) || (buf_addr & (buf_len -1)))
Ditto.
dst_maxburst = 1;
else
dst_maxburst = STM32_DMA_MAX_BURST;
With these fixes, you can add my
Reviewed-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
Tested-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
Regards,
Amelie
