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

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Message-ID: <20251201-calamity-favoring-b2d1ec4bcc81@spud>
Date: Mon, 1 Dec 2025 16:08:57 +0000
From: Conor Dooley <conor@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Jonas Gorski <jonas.gorski@...il.com>,
	Prajna Rajendra Kumar <prajna.rajendrakumar@...rochip.com>,
	Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] spi: microchip-core: use XOR instead of ANDNOT to
 simplify the logic

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@...ux.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.
FWIW:
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

Cheers,
Conor.

> 
> > >                 dev_err(&spi->dev, "incompatible CPOL/CPHA, must match controller's Motorola mode\n");
> > >                 return -EINVAL;
> > >         }
> 
> Thanks for the review!
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

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