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[141.94.163.193]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-44a98b768fdsm4823539f8f.33.2026.05.01.07.00.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 May 2026 07:00:00 -0700 (PDT) From: John Madieu To: broonie@kernel.org, Frank.Li@nxp.com, s.hauer@pengutronix.de Cc: kernel@pengutronix.de, festevam@gmail.com, carlos.song@nxp.com, linux-spi@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, John Madieu Subject: [PATCH 1/3] spi: imx: Fix precedence bug in spi_imx_dma_max_wml_find() Date: Fri, 1 May 2026 13:59:49 +0000 Message-Id: <20260501135951.2416527-2-john.madieu@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260501135951.2416527-1-john.madieu@gmail.com> References: <20260501135951.2416527-1-john.madieu@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- drivers/spi/spi-imx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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 */ -- 2.25.1