linux-kernel - Re: [PATCH v5 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux

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Date:   Tue, 12 May 2020 14:28:25 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Dave Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Sandeep Panda <spanda@...eaurora.org>,
        Jonas Karlman <jonas@...boo.se>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        MSM <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux

On Thu, May 7, 2020 at 11:35 PM Douglas Anderson <dianders@...omium.org> wrote:

> The ti-sn65dsi86 MIPI DSI to eDP bridge chip has 4 pins on it that can
> be used as GPIOs in a system.  Each pin can be configured as input,
> output, or a special function for the bridge chip.  These are:
> - GPIO1: SUSPEND Input
> - GPIO2: DSIA VSYNC
> - GPIO3: DSIA HSYNC or VSYNC
> - GPIO4: PWM
>
> Let's expose these pins as GPIOs.  A few notes:
> - Access to ti-sn65dsi86 is via i2c so we set "can_sleep".
> - These pins can't be configured for IRQ.
> - There are no programmable pulls or other fancy features.
> - Keeping the bridge chip powered might be expensive.  The driver is
>   setup such that if all used GPIOs are only inputs we'll power the
>   bridge chip on just long enough to read the GPIO and then power it
>   off again.  Setting a GPIO as output will keep the bridge powered.
> - If someone releases a GPIO we'll implicitly switch it to an input so
>   we no longer need to keep the bridge powered for it.
>
> Because of all of the above limitations we just need to implement a
> bare-bones GPIO driver.  The device tree bindings already account for
> this device being a GPIO controller so we only need the driver changes
> for it.
>
> NOTE: Despite the fact that these pins are nominally muxable I don't
> believe it makes sense to expose them through the pinctrl interface as
> well as the GPIO interface.  The special functions are things that the
> bridge chip driver itself would care about and it can just configure
> the pins as needed.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Bartosz Golaszewski <bgolaszewski@...libre.com>

Looks good mostly!

> +       pdata->gchip.label = dev_name(pdata->dev);
> +       pdata->gchip.parent = pdata->dev;
> +       pdata->gchip.owner = THIS_MODULE;
> +       pdata->gchip.of_xlate = tn_sn_bridge_of_xlate;
> +       pdata->gchip.of_gpio_n_cells = 2;
> +       pdata->gchip.free = ti_sn_bridge_gpio_free;
> +       pdata->gchip.get_direction = ti_sn_bridge_gpio_get_direction;
> +       pdata->gchip.direction_input = ti_sn_bridge_gpio_direction_input;
> +       pdata->gchip.direction_output = ti_sn_bridge_gpio_direction_output;
> +       pdata->gchip.get = ti_sn_bridge_gpio_get;
> +       pdata->gchip.set = ti_sn_bridge_gpio_set;
> +       pdata->gchip.can_sleep = true;
> +       pdata->gchip.names = ti_sn_bridge_gpio_names;
> +       pdata->gchip.ngpio = SN_NUM_GPIOS;

Please add:
pdata->gchip.base = -1;

So it is clear that you use dynamically assigned GPIO numbers,
with that:
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij