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Commit 2c99fd57 authored by Stefan Wahren's avatar Stefan Wahren Committed by Greg Kroah-Hartman
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spi: spi-fsl-lpspi: Fix scldiv calculation 



[ 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: 5314987d ("spi: imx: add lpspi bus driver")
Signed-off-by: default avatarStefan Wahren <wahrenst@gmx.net>
Link: https://patch.msgid.link/20240804113611.83613-1-wahrenst@gmx.net


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 3a5e84e6

drivers/spi/spi-fsl-lpspi.c

+4 −2
Original line number Diff line number Diff line
@@ -317,7 +317,7 @@ 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);
@@ -328,8 +328,10 @@ 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;