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

[Amelie Delaunay]

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.

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>
---
 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