From: Linus Walleij <linus.walleij@linaro.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Dave Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Rob Herring <robh+dt@kernel.org>,
Neil Armstrong <narmstrong@baylibre.com>,
Andrzej Hajda <a.hajda@samsung.com>,
Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
Sandeep Panda <spanda@codeaurora.org>,
Stephen Boyd <swboyd@chromium.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
Jeffrey Hugo <jeffrey.l.hugo@gmail.com>,
"open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
MSM <linux-arm-msm@vger.kernel.org>,
Rob Clark <robdclark@chromium.org>,
Jernej Skrabec <jernej.skrabec@siol.net>,
Jonas Karlman <jonas@kwiboo.se>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux
Date: Tue, 28 Apr 2020 14:44:09 +0200 [thread overview]
Message-ID: <CACRpkdYsw1uFf_PVkRwibXUtQOwvWa7jqiw6aT9AdmkLLyqisQ@mail.gmail.com> (raw)
In-Reply-To: <20200423092431.v3.1.Ia50267a5549392af8b37e67092ca653a59c95886@changeid>
On Thu, Apr 23, 2020 at 6:26 PM Douglas Anderson <dianders@chromium.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@chromium.org>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Pretty cool.
I wonder if this chip could use the generic regmap GPIO helpers
that we are working on when they come around?
https://lore.kernel.org/linux-gpio/20200423174543.17161-11-michael@walle.cc/
> +#include <linux/gpio/driver.h>
> +#include <linux/gpio.h>
Only <linux/gpio/driver.h> should be needed else you are doing
something wrong.
> + * @gchip: If we expose our GPIOs, this is used.
> + * @gchip_output: A cache of whether we've set GPIOs to output. This
> + * serves double-duty of keeping track of the direction and
> + * also keeping track of whether we've incremented the
> + * pm_runtime reference count for this pin, which we do
> + * whenever a pin is configured as an output.
That sounds a bit hairy but I guess it's fine.
> + */
> struct ti_sn_bridge {
> struct device *dev;
> struct regmap *regmap;
> @@ -102,6 +136,9 @@ struct ti_sn_bridge {
> struct gpio_desc *enable_gpio;
> struct regulator_bulk_data supplies[SN_REGULATOR_SUPPLY_NUM];
> int dp_lanes;
> +
> + struct gpio_chip gchip;
> + DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS);
Do you really need a bitmap for 4 bits? Can't you just have something
like an u8 and check bit 0,1,2,3 ... well I suppose it has some elegance to
it as well but... hm.
> +static struct ti_sn_bridge *gchip_to_pdata(struct gpio_chip *chip)
> +{
> + return container_of(chip, struct ti_sn_bridge, gchip);
> +}
> +
> +static int ti_sn_bridge_gpio_get_direction(struct gpio_chip *chip,
> + unsigned int offset)
> +{
> + struct ti_sn_bridge *pdata = gchip_to_pdata(chip);
Is there some specific reason why you don't just use
gpiochip_get_data()?
> + /*
> + * We already have to keep track of the direction because we use
> + * that to figure out whether we've powered the device. We can
> + * just return that rather than (maybe) powering up the device
> + * to ask its direction.
> + */
> + return test_bit(offset, pdata->gchip_output) ?
> + GPIOF_DIR_OUT : GPIOF_DIR_IN;
> +}
Don't use these legacy defines, they are for consumers.
Use GPIO_LINE_DIRECTION_IN and GPIO_LINE_DIRECTION_OUT.
from <linux/gpio/driver.h>
> + ret = regmap_read(pdata->regmap, SN_GPIO_IO_REG, &val);
> + pm_runtime_put(pdata->dev);
> +
> + if (ret)
> + return ret;
> +
> + return (val >> (SN_GPIO_INPUT_SHIFT + offset)) & 1;
My preferred way to do this is:
#include <linux/bits.h>
return !!(val & BIT(SN_GPIO_INPUT_SHIFT + offset));
> +static void ti_sn_bridge_gpio_set(struct gpio_chip *chip, unsigned int offset,
> + int val)
> +{
> + struct ti_sn_bridge *pdata = gchip_to_pdata(chip);
> + int ret;
> +
> + if (!test_bit(offset, pdata->gchip_output)) {
> + dev_err(pdata->dev, "Ignoring GPIO set while input\n");
> + return;
> + }
> +
> + val &= 1;
> + ret = regmap_update_bits(pdata->regmap, SN_GPIO_IO_REG,
> + BIT(SN_GPIO_OUTPUT_SHIFT + offset),
> + val << (SN_GPIO_OUTPUT_SHIFT + offset));
Looks like a job for the generic helper library.
> +static int ti_sn_bridge_gpio_direction_input(struct gpio_chip *chip,
> + unsigned int offset)
> +{
> + struct ti_sn_bridge *pdata = gchip_to_pdata(chip);
> + int shift = offset * 2;
> + int ret;
> +
> + if (!test_and_clear_bit(offset, pdata->gchip_output))
> + return 0;
> +
> + ret = regmap_update_bits(pdata->regmap, SN_GPIO_CTRL_REG,
> + 0x3 << shift, SN_GPIO_MUX_INPUT << shift);
But this 0x03 does not look very generic, it's not just 1 bit but 2.
Overall it looks good, just the minor things above need fixing or
looking into.
Yours,
Linus Walleij
next prev parent reply other threads:[~2020-04-28 12:44 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 16:25 [PATCH v3 0/6] drm: Prepare to use a GPIO on ti-sn65dsi86 for Hot Plug Detect Douglas Anderson
2020-04-23 16:25 ` [PATCH v3 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux Douglas Anderson
2020-04-25 19:38 ` Stephen Boyd
2020-04-28 12:44 ` Linus Walleij [this message]
2020-04-29 0:45 ` Doug Anderson
2020-04-23 16:25 ` [PATCH v3 2/6] dt-bindings: display: Add hpd-gpios to panel-common bindings Douglas Anderson
2020-04-28 12:17 ` Linus Walleij
2020-04-23 16:25 ` [PATCH v3 3/6] drm/panel-simple: Support hpd-gpios for delaying prepare() Douglas Anderson
2020-04-28 12:21 ` Linus Walleij
2020-04-23 16:25 ` [PATCH v3 4/6] dt-bindings: drm/bridge: ti-sn65dsi86: Convert to yaml Douglas Anderson
2020-04-25 19:32 ` Stephen Boyd
2020-04-23 16:25 ` [PATCH v3 5/6] dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd Douglas Anderson
2020-04-28 12:25 ` Linus Walleij
2020-04-23 16:25 ` [PATCH v3 6/6] arm64: dts: sdm845: Add "no-hpd" to sn65dsi86 on cheza Douglas Anderson
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