Re: [PATCH v4 2/2] spi: microchip-core: use XOR instead of ANDNOT to simplify the logic

Jonas Gorski
2025-11-28T19:30:56Z

On Fri, Nov 28, 2025 at 7:56 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> Use XOR instead of ANDNOT to simplify the logic. The current approach
> with (foo & BAR & ~baz) is harder to process than more usual pattern
> for the comparing misconfiguration using ((foo ^ baz) & BAR) which
> can be read as "find all different bits between foo and baz that are
> related to BAR (mask)". Besides that it makes binary code shorter.
>
> Function old new delta
> mchp_corespi_setup 103 99 -4
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> drivers/spi/spi-microchip-core-spi.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-microchip-core-spi.c b/drivers/spi/spi-microchip-core-spi.c
> index 98bf0e6cd00e..2f4b21ad56a7 100644
> --- a/drivers/spi/spi-microchip-core-spi.c
> +++ b/drivers/spi/spi-microchip-core-spi.c
> @@ -161,7 +161,7 @@ static int mchp_corespi_setup(struct spi_device *spi)
> return -EOPNOTSUPP;
> }
>
> - if (spi->mode & SPI_MODE_X_MASK & ~spi->controller->mode_bits) {
> + if ((spi->mode ^ spi->controller->mode_bits) & SPI_MODE_X_MASK) {

This changes the behavior: if a bit isn't set in spi->mode that is set
in mode_bits, it would have been previously accepted, now it's
refused. E.g. controller has (SPI_CPOL | SPI_CPHA), device only
SPI_CPOL. 0x1 & 0x3 & ~0x3 => 0, vs (0x1 ^ 0x3) & 0x3 => 0x2

If this is the actually intended behavior here, it is a fix and should
carry a Fixes tag (the message below implies that).

> dev_err(&spi->dev, "incompatible CPOL/CPHA, must match controller's Motorola mode\n");
> return -EINVAL;
> }

Best regards,
Jonas