dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width

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@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20211103153312.41483-1-amelie.delaunay@foss.st.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 2283c50..83a37a6 100644 (file)
--- 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;