linux-kernel - Re: [PATCH v1] spi: fix client driver breakages when using GPIO descriptors

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Date:   Mon, 9 Nov 2020 16:25:10 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Simon Han <z.han@...bus.com>, Lukas Wunner <lukas@...ner.de>,
        linux-spi <linux-spi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] spi: fix client driver breakages when using GPIO descriptors

On Fri, Nov 6, 2020 at 5:08 PM Sven Van Asbroeck <thesven73@...il.com> wrote:
>
> From: Sven Van Asbroeck <thesven73@...il.com>
>
> Commit f3186dd87669 ("spi: Optionally use GPIO descriptors for CS GPIOs")
> introduced the optional use of GPIO descriptors for chip selects.
>
> A side-effect of this change: when a SPI bus uses GPIO descriptors,
> all its client devices have SPI_CS_HIGH set in spi->mode. This flag is
> required for the SPI bus to operate correctly.
>
> This unfortunately breaks many client drivers, which use the following
> pattern to configure their underlying SPI bus:
>
> static int client_device_probe(struct spi_device *spi)
> {
>         ...
>         spi->mode = SPI_MODE_0;
>         spi->bits_per_word = 8;
>         err = spi_setup(spi);
>         ..
> }
>
> In short, many client drivers overwrite the SPI_CS_HIGH bit in
> spi->mode, and break the underlying SPI bus driver.

Sounds like "many SPI drivers have to be fixed".



-- 
With Best Regards,
Andy Shevchenko