[PATCH 1/3] spi: imx: Fix precedence bug in spi_imx_dma_max_wml_find()

[John Madieu]

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 <john.madieu@xxxxxxxxx>
---
 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