From: John Madieu Date: Fri, 1 May 2026 13:59:49 +0000 (+0000) Subject: spi: imx: Fix precedence bug in spi_imx_dma_max_wml_find() X-Git-Tag: v7.1-rc3~21^2~2^2~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=24e0fd8b852062d5e8a740f7945eaa26818adce8;p=thirdparty%2Fkernel%2Flinux.git spi: imx: Fix precedence bug in spi_imx_dma_max_wml_find() The watermark search in spi_imx_dma_max_wml_find() reads: if (!dma_data->dma_len % (i * bytes_per_word)) break; The unary ! binds tighter than %, so this parses as: if ((!dma_data->dma_len) % (i * bytes_per_word)) break; !dma_data->dma_len is 0 or 1, and `0 % x == 0` for any x; `1 % x` is 0 unless x == 1. The condition is therefore false in every case except dma_len != 0 with i * bytes_per_word == 1, i.e. i == 1 and bytes_per_word == 1. The loop almost always falls through to its end, leaving i == 0, which the post-loop fallback rewrites to 1: if (i == 0) i = 1; So spi_imx->wml ends up at 1 for essentially every DMA transfer, defeating the entire purpose of the function. The DMA engine then requests service after every single FIFO word instead of using multi-word bursts, hurting throughput on every DMA-capable variant. Add the missing parentheses so the modulo is computed first, then negated: if (!(dma_data->dma_len % (i * bytes_per_word))) break; Fixes: faa8e404ad8e ("spi: imx: support dynamic burst length for ECSPI DMA mode") Signed-off-by: John Madieu Reviewed-by: Frank Li Link: https://patch.msgid.link/20260501135951.2416527-2-john.madieu@gmail.com Signed-off-by: Mark Brown --- diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index e5c907c45b87..7ae8078c10ef 100644 --- a/drivers/spi/spi-imx.c +++ b/drivers/spi/spi-imx.c @@ -1836,7 +1836,7 @@ static void spi_imx_dma_max_wml_find(struct spi_imx_data *spi_imx, unsigned int i; for (i = spi_imx->devtype_data->fifo_size / 2; i > 0; i--) { - if (!dma_data->dma_len % (i * bytes_per_word)) + if (!(dma_data->dma_len % (i * bytes_per_word))) break; } /* Use 1 as wml in case no available burst length got */