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: <12446fa2-570b-4882-80dc-c72a166aaf19@microchip.com>
Date: Thu, 8 Jan 2026 13:00:39 +0000
From: Prajna Rajendra Kumar <prajna.rajendrakumar@...rochip.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Conor Dooley
	<conor@...nel.org>
CC: Jonas Gorski <jonas.gorski@...il.com>, Mark Brown <broonie@...nel.org>,
	<linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Prajna Rajendra
 Kumar - M74368" <prajna.rajendrakumar@...rochip.com>
Subject: Re: [PATCH v4 2/2] spi: microchip-core: use XOR instead of ANDNOT to
 simplify the logic

On 01/12/2025 17:57, Andy Shevchenko wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>
> 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@...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.
> Okay, let's not hurry up with this and wait for testing results.
>
>> FWIW:
>> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
>>>>>                  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
>
>
Hi,

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@...rochip.com>