6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stefan Wahren <wahrenst@xxxxxxx>
[ Upstream commit 730bbfaf7d4890bd99e637db7767dc68cfeb24e7 ]
The effective SPI clock frequency should never exceed speed_hz
otherwise this might result in undefined behavior of the SPI device.
Currently the scldiv calculation could violate this constraint.
For the example parameters perclk_rate = 24 MHz and speed_hz = 7 MHz,
the function fsl_lpspi_set_bitrate will determine perscale = 0 and
scldiv = 1, which is a effective SPI clock of 8 MHz.
So fix this by rounding up the quotient of perclk_rate and speed_hz.
While this never change within the loop, we can pull this out.
Fixes: 5314987de5e5 ("spi: imx: add lpspi bus driver")
Signed-off-by: Stefan Wahren <wahrenst@xxxxxxx>
Link: https://patch.msgid.link/20240804113611.83613-1-wahrenst@xxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/spi/spi-fsl-lpspi.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/spi/spi-fsl-lpspi.c b/drivers/spi/spi-fsl-lpspi.c
index 9e324d72596af..dd2381ac27f67 100644
--- a/drivers/spi/spi-fsl-lpspi.c
+++ b/drivers/spi/spi-fsl-lpspi.c
@@ -297,7 +297,7 @@ static void fsl_lpspi_set_watermark(struct fsl_lpspi_data *fsl_lpspi)
static int fsl_lpspi_set_bitrate(struct fsl_lpspi_data *fsl_lpspi)
{
struct lpspi_config config = fsl_lpspi->config;
- unsigned int perclk_rate, scldiv;
+ unsigned int perclk_rate, scldiv, div;
u8 prescale;
perclk_rate = clk_get_rate(fsl_lpspi->clk_per);
@@ -308,8 +308,10 @@ static int fsl_lpspi_set_bitrate(struct fsl_lpspi_data *fsl_lpspi)
return -EINVAL;
}
+ div = DIV_ROUND_UP(perclk_rate, config.speed_hz);
+
for (prescale = 0; prescale < 8; prescale++) {
- scldiv = perclk_rate / config.speed_hz / (1 << prescale) - 2;
+ scldiv = div / (1 << prescale) - 2;
if (scldiv < 256) {
fsl_lpspi->config.prescale = prescale;
break;
--
2.43.0
