linux-kernel - Re: [PATCH v2 5/5] drm/solomon: Add SSD130x OLED displays SPI support

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Message-ID: <CAMuHMdWsmtBdcV=LL4yqprtbum4f9cSu8orjoPACECa5QENmsg@mail.gmail.com>
Date:   Tue, 12 Apr 2022 09:31:09 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Chen-Yu Tsai <wens@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maxime Ripard <maxime@...no.tech>,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH v2 5/5] drm/solomon: Add SSD130x OLED displays SPI support

Hi Javier,

On Mon, Apr 11, 2022 at 11:12 PM Javier Martinez Canillas
<javierm@...hat.com> wrote:
> The ssd130x driver only provides the core support for these devices but it
> does not have any bus transport logic. Add a driver to interface over SPI.
>
> There is a difference in the communication protocol when using 4-wire SPI
> instead of I2C. For the latter, a control byte that contains a D/C# field
> has to be sent. This field tells the controller whether the data has to be
> written to the command register or to the graphics display data memory.
>
> But for 4-wire SPI that control byte is not used, instead a real D/C# line
> must be pulled HIGH for commands data and LOW for graphics display data.
>
> For this reason the standard SPI regmap can't be used and a custom .write
> bus handler is needed.
>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> Acked-by: Mark Brown <broonie@...nel.org>

Thanks for your patch!

> --- /dev/null
> +++ b/drivers/gpu/drm/solomon/ssd130x-spi.c

> +static struct gpio_desc *ssd130x_spi_get_dc(struct device *dev)
> +{
> +       struct gpio_desc *dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_LOW);
> +
> +       if (IS_ERR(dc))
> +               return ERR_PTR(dev_err_probe(dev, PTR_ERR(dc), "Failed to get dc gpio\n"));
> +
> +       return dc;
> +}
> +
> +static int ssd130x_spi_probe(struct spi_device *spi)
> +{
> +       struct ssd130x_spi_transport *t;
> +       struct ssd130x_device *ssd130x;
> +       struct regmap *regmap;
> +       struct device *dev = &spi->dev;
> +
> +       t = devm_kzalloc(dev, sizeof(*t), GFP_KERNEL);
> +       if (!t)
> +               return dev_err_probe(dev, -ENOMEM,
> +                                    "Failed to allocate SPI transport data\n");
> +
> +       t->spi = spi;
> +
> +       t->dc = ssd130x_spi_get_dc(&spi->dev);
> +       if (IS_ERR(t->dc))
> +               return PTR_ERR(t->dc);

This can be simplified (no need for the PTR_ERR(ERR_PTR(...) dance)
by open-coding ssd130x_spi_get_dc() here.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds