Re: [PATCH 1/3] spi: spi-fsl-lpspi: Adjust type of scldiv

[Frank Li <Frank.li@xxxxxxx>]

On Mon, Sep 30, 2024 at 11:30:54AM +0200, Stefan Wahren wrote:
> The target value of scldiv is just a byte, but its calculation in
> fsl_lpspi_set_bitrate could be negative. So use an adequate type to store
> the result and avoid overflows. After that this needs range check
> adjustments, but this should make the code less opaque.
>
> Signed-off-by: Stefan Wahren <wahrenst@xxxxxxx>
> ---
Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
>  drivers/spi/spi-fsl-lpspi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/spi/spi-fsl-lpspi.c b/drivers/spi/spi-fsl-lpspi.c
> index 977e8b55c82b..196cc68f2057 100644
> --- a/drivers/spi/spi-fsl-lpspi.c
> +++ b/drivers/spi/spi-fsl-lpspi.c
> @@ -315,9 +315,10 @@ 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, div;
> +	unsigned int perclk_rate, div;
>  	u8 prescale_max;
>  	u8 prescale;
> +	int scldiv;
>
>  	perclk_rate = clk_get_rate(fsl_lpspi->clk_per);
>  	prescale_max = fsl_lpspi->devtype_data->prescale_max;
> @@ -338,13 +339,13 @@ static int fsl_lpspi_set_bitrate(struct fsl_lpspi_data *fsl_lpspi)
>
>  	for (prescale = 0; prescale <= prescale_max; prescale++) {
>  		scldiv = div / (1 << prescale) - 2;
> -		if (scldiv < 256) {
> +		if (scldiv >= 0 && scldiv < 256) {
>  			fsl_lpspi->config.prescale = prescale;
>  			break;
>  		}
>  	}
>
> -	if (scldiv >= 256)
> +	if (scldiv < 0 || scldiv >= 256)
>  		return -EINVAL;
>
>  	writel(scldiv | (scldiv << 8) | ((scldiv >> 1) << 16),
> --
> 2.34.1
>