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    Subject[PATCH 5.14 768/849] dmaengine: stm32-dma: avoid 64-bit division in stm32_dma_get_max_width
    Date
    From: Arnd Bergmann <arnd@arndb.de>

    [ 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@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>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 1b2063fb3d1d6..bf3042b655485 100644
    --- a/drivers/dma/stm32-dma.c
    +++ b/drivers/dma/stm32-dma.c
    @@ -278,7 +278,7 @@ 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;
    @@ -754,7 +754,7 @@ 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;
    @@ -810,7 +810,7 @@ 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;
    --
    2.33.0


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