[PATCH v3] spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock

[Marek Vasut]

On 11/15/22 19:10, Frieder Schrempf wrote:
> From: Frieder Schrempf <frieder.schrempf at kontron.de>
> 
> In case the requested bus clock is higher than the input clock, the correct
> dividers (pre = 0, post = 0) are returned from mx51_ecspi_clkdiv(), but
> *fres is left uninitialized and therefore contains an arbitrary value.
> 
> This causes trouble for the recently introduced PIO polling feature as the
> value in spi_imx->spi_bus_clk is used there to calculate for which
> transfers to enable PIO polling.
> 
> Fix this by setting *fres even if no clock dividers are in use.
> 
> This issue was observed on Kontron BL i.MX8MM with an SPI peripheral clock set
> to 50 MHz by default and a requested SPI bus clock of 80 MHz for the SPI NOR
> flash.
> 
> With the fix applied the debug message from mx51_ecspi_clkdiv() now prints the
> following:
> 
> spi_imx 30820000.spi: mx51_ecspi_clkdiv: fin: 50000000, fspi: 50000000,
> post: 0, pre: 0
> 
> Fixes: 6fd8b8503a0d ("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds")
> Fixes: 07e759387788 ("spi: spi-imx: add PIO polling support")
> Cc: Marc Kleine-Budde <mkl at pengutronix.de>
> Cc: David Jander <david at protonic.nl>
> Cc: Fabio Estevam <festevam at gmail.com>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Marek Vasut <marex at denx.de>
> Cc: stable at vger.kernel.org
> Signed-off-by: Frieder Schrempf <frieder.schrempf at kontron.de>
> Tested-by: Fabio Estevam <festevam at gmail.com>
> ---
> 
> Changes for v3:
> 
> * Add back the Fixes tag for commit 6fd8b8503a0d
> * Add Fabio's Tested-by (Thanks!)
> 
> Changes for v2:
> 
> * Remove the reference and the Fixes tag for commit 6fd8b8503a0d as it is
>    incorrect.
> ---
>   drivers/spi/spi-imx.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index 30d82cc7300b..468ce0a2b282 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -444,8 +444,7 @@ static unsigned int mx51_ecspi_clkdiv(struct spi_imx_data *spi_imx,
>   	unsigned int pre, post;
>   	unsigned int fin = spi_imx->spi_clk;
>   
> -	if (unlikely(fspi > fin))
> -		return 0;
> +	fspi = min(fspi, fin);
>   
>   	post = fls(fin) - fls(fspi);
>   	if (fin > fspi << post)

Can you also test the SPI flash at some 100 kHz, just to see whether it 
still works properly ? (to retain behavior fixed first in 6fd8b8503a0dc 
("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds") )

The fix here does look fine by me however.