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

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Thu, Jan 08, 2026 at 01:00:39PM +0000, Prajna Rajendra Kumar wrote:
> On 01/12/2025 17:57, Andy Shevchenko wrote:
> > On Mon, Dec 01, 2025 at 04:08:57PM +0000, Conor Dooley wrote:
> > > On Sat, Nov 29, 2025 at 10:19:00AM +0200, Andy Shevchenko wrote:
> > > > On Fri, Nov 28, 2025 at 08:30:43PM +0100, Jonas Gorski wrote:
> > > > > On Fri, Nov 28, 2025 at 7:56 PM Andy Shevchenko
> > > > > <andriy.shevchenko@linux.intel.com> wrote:

...

> > > > > > -       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).
> > > > Yeah, yesterday I was thinking about the same and I was confused by the logic
> > > > behind. As far as I understood the comments regarding mode provided by DT is
> > > > that the mode is configured in IP and may not be changed. And you are right
> > > > about the fix, but let's wait for Microchip to elaborate on the expected
> > > > behaviour.
> > > Prajna is on holiday and I don't have a setup to actually test this on,
> > > but I'm 99% sure that you're both right and the original behaviour was
> > > wrong. There's a verilog parameter to the IP block that determines which
> > > motorola mode it is and a device that's not an exact match won't work.
> > Okay, let's not hurry up with this and wait for testing results.
> > 
> > > FWIW:
> > > Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > > > > >                  dev_err(&spi->dev, "incompatible CPOL/CPHA, must match controller's Motorola mode\n");
> > > > > >                  return -EINVAL;
> > > > > >          }
> > Thanks for the review!
> 
> I've tested this on my setup and XOR check matches how the controller
> behaves. The SPI mode is fixed in hardware, so the previous logic was
> wrong.
> 
> Tested-by: Prajna Rajendra Kumar <prajna.rajendrakumar@microchip.com>

Thank you! I just sent a new version of this patch with updated tags and commit
message.

-- 
With Best Regards,
Andy Shevchenko