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Date:   Mon, 11 May 2020 18:36:46 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     linus.walleij@...aro.org, bgolaszewski@...libre.com,
        airlied@...ux.ie, daniel@...ll.ch, robh+dt@...nel.org,
        narmstrong@...libre.com, a.hajda@...sung.com,
        Laurent.pinchart@...asonboard.com, spanda@...eaurora.org,
        jonas@...boo.se, jeffrey.l.hugo@...il.com,
        linux-gpio@...r.kernel.org, swboyd@...omium.org,
        jernej.skrabec@...l.net, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        robdclark@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to
 Linux

On Thu 07 May 14:34 PDT 2020, Douglas Anderson 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.
> 

I'm working on a patch for supporting the PWM controller in the bridge
and as you say the muxing for that is better left internal to the bridge
driver.

> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Bartosz Golaszewski <bgolaszewski@...libre.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
> Removed Stephen's review tag in v5 to confirm he's good with the way I
> implemented of_xlate.
> 
> Changes in v5:
> - Use of_xlate so that numbers in dts start at 1, not 0.
> 
> Changes in v4:
> - Don't include gpio.h
> - Use gpiochip_get_data() instead of container_of() to get data.
> - GPIOF_DIR_XXX => GPIO_LINE_DIRECTION_XXX
> - Use Linus W's favorite syntax to read a bit from a bitfield.
> - Define and use SN_GPIO_MUX_MASK.
> - Add a comment about why we use a bitmap for gchip_output.
> 
> Changes in v3:
> - Becaue => Because
> - Add a kernel-doc to our pdata to clarify double-duty of gchip_output.
> - More comments about how powering off affects us (get_dir, dir_input).
> - Cleanup tail of ti_sn_setup_gpio_controller() to avoid one "return".
> - Use a bitmap rather than rolling my own.
> 
> Changes in v2:
> - ("Export...GPIOs") is 1/2 of replacement for ("Allow...bridge GPIOs")
> 
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 214 ++++++++++++++++++++++++++
>  1 file changed, 214 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 6ad688b320ae..4e8df948b3b8 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -4,9 +4,11 @@
>   * datasheet: http://www.ti.com/lit/ds/symlink/sn65dsi86.pdf
>   */
>  
> +#include <linux/bits.h>
>  #include <linux/clk.h>
>  #include <linux/debugfs.h>
>  #include <linux/gpio/consumer.h>
> +#include <linux/gpio/driver.h>
>  #include <linux/i2c.h>
>  #include <linux/iopoll.h>
>  #include <linux/module.h>
> @@ -54,6 +56,14 @@
>  #define  BPP_18_RGB				BIT(0)
>  #define SN_HPD_DISABLE_REG			0x5C
>  #define  HPD_DISABLE				BIT(0)
> +#define SN_GPIO_IO_REG				0x5E
> +#define  SN_GPIO_INPUT_SHIFT			4
> +#define  SN_GPIO_OUTPUT_SHIFT			0
> +#define SN_GPIO_CTRL_REG			0x5F
> +#define  SN_GPIO_MUX_INPUT			0
> +#define  SN_GPIO_MUX_OUTPUT			1
> +#define  SN_GPIO_MUX_SPECIAL			2
> +#define  SN_GPIO_MUX_MASK			0x3
>  #define SN_AUX_WDATA_REG(x)			(0x64 + (x))
>  #define SN_AUX_ADDR_19_16_REG			0x74
>  #define SN_AUX_ADDR_15_8_REG			0x75
> @@ -88,6 +98,35 @@
>  
>  #define SN_REGULATOR_SUPPLY_NUM		4
>  
> +#define SN_NUM_GPIOS			4
> +#define SN_GPIO_PHYSICAL_OFFSET		1
> +
> +/**
> + * struct ti_sn_bridge - Platform data for ti-sn65dsi86 driver.
> + * @dev:          Pointer to our device.
> + * @regmap:       Regmap for accessing i2c.
> + * @aux:          Our aux channel.
> + * @bridge:       Our bridge.
> + * @connector:    Our connector.
> + * @debugfs:      Used for managing our debugfs.
> + * @host_node:    Remote DSI node.
> + * @dsi:          Our MIPI DSI source.
> + * @refclk:       Our reference clock.
> + * @panel:        Our panel.
> + * @enable_gpio:  The GPIO we toggle to enable the bridge.
> + * @supplies:     Data for bulk enabling/disabling our regulators.
> + * @dp_lanes:     Count of dp_lanes we're using.
> + *
> + * @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.  This is a
> + *                bitmap so we can do atomic ops on it without an extra
> + *                lock so concurrent users of our 4 GPIOs don't stomp on
> + *                each other's read-modify-write.
> + */
>  struct ti_sn_bridge {
>  	struct device			*dev;
>  	struct regmap			*regmap;
> @@ -102,6 +141,9 @@ 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);
>  };
>  
>  static const struct regmap_range ti_sn_bridge_volatile_ranges[] = {
> @@ -874,6 +916,172 @@ static int ti_sn_bridge_parse_dsi_host(struct ti_sn_bridge *pdata)
>  	return 0;
>  }
>  
> +static int tn_sn_bridge_of_xlate(struct gpio_chip *chip,
> +				 const struct of_phandle_args *gpiospec,
> +				 u32 *flags)
> +{
> +	if (WARN_ON(gpiospec->args_count < chip->of_gpio_n_cells))
> +		return -EINVAL;
> +
> +	if (gpiospec->args[0] > chip->ngpio || gpiospec->args[0] < 1)
> +		return -EINVAL;
> +
> +	if (flags)
> +		*flags = gpiospec->args[1];
> +
> +	return gpiospec->args[0] - SN_GPIO_PHYSICAL_OFFSET;
> +}
> +
> +static int ti_sn_bridge_gpio_get_direction(struct gpio_chip *chip,
> +					   unsigned int offset)
> +{
> +	struct ti_sn_bridge *pdata = gpiochip_get_data(chip);
> +
> +	/*
> +	 * 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) ?
> +		GPIO_LINE_DIRECTION_OUT : GPIO_LINE_DIRECTION_IN;
> +}
> +
> +static int ti_sn_bridge_gpio_get(struct gpio_chip *chip, unsigned int offset)
> +{
> +	struct ti_sn_bridge *pdata = gpiochip_get_data(chip);
> +	unsigned int val;
> +	int ret;
> +
> +	/*
> +	 * When the pin is an input we don't forcibly keep the bridge
> +	 * powered--we just power it on to read the pin.  NOTE: part of
> +	 * the reason this works is that the bridge defaults (when
> +	 * powered back on) to all 4 GPIOs being configured as GPIO input.
> +	 * Also note that if something else is keeping the chip powered the
> +	 * pm_runtime functions are lightweight increments of a refcount.
> +	 */
> +	pm_runtime_get_sync(pdata->dev);
> +	ret = regmap_read(pdata->regmap, SN_GPIO_IO_REG, &val);
> +	pm_runtime_put(pdata->dev);
> +
> +	if (ret)
> +		return ret;
> +
> +	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 = gpiochip_get_data(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));
> +}
> +
> +static int ti_sn_bridge_gpio_direction_input(struct gpio_chip *chip,
> +					     unsigned int offset)
> +{
> +	struct ti_sn_bridge *pdata = gpiochip_get_data(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,
> +				 SN_GPIO_MUX_MASK << shift,
> +				 SN_GPIO_MUX_INPUT << shift);
> +	if (ret) {
> +		set_bit(offset, pdata->gchip_output);
> +		return ret;
> +	}
> +
> +	/*
> +	 * NOTE: if nobody else is powering the device this may fully power
> +	 * it off and when it comes back it will have lost all state, but
> +	 * that's OK because the default is input and we're now an input.
> +	 */
> +	pm_runtime_put(pdata->dev);
> +
> +	return 0;
> +}
> +
> +static int ti_sn_bridge_gpio_direction_output(struct gpio_chip *chip,
> +					      unsigned int offset, int val)
> +{
> +	struct ti_sn_bridge *pdata = gpiochip_get_data(chip);
> +	int shift = offset * 2;
> +	int ret;
> +
> +	if (test_and_set_bit(offset, pdata->gchip_output))
> +		return 0;
> +
> +	pm_runtime_get_sync(pdata->dev);
> +
> +	/* Set value first to avoid glitching */
> +	ti_sn_bridge_gpio_set(chip, offset, val);
> +
> +	/* Set direction */
> +	ret = regmap_update_bits(pdata->regmap, SN_GPIO_CTRL_REG,
> +				 SN_GPIO_MUX_MASK << shift,
> +				 SN_GPIO_MUX_OUTPUT << shift);
> +	if (ret) {
> +		clear_bit(offset, pdata->gchip_output);
> +		pm_runtime_put(pdata->dev);
> +	}
> +
> +	return ret;
> +}
> +
> +static void ti_sn_bridge_gpio_free(struct gpio_chip *chip, unsigned int offset)
> +{
> +	/* We won't keep pm_runtime if we're input, so switch there on free */
> +	ti_sn_bridge_gpio_direction_input(chip, offset);
> +}
> +
> +static const char * const ti_sn_bridge_gpio_names[SN_NUM_GPIOS] = {
> +	"GPIO1", "GPIO2", "GPIO3", "GPIO4"
> +};
> +
> +static int ti_sn_setup_gpio_controller(struct ti_sn_bridge *pdata)
> +{
> +	int ret;
> +
> +	/* Only init if someone is going to use us as a GPIO controller */
> +	if (!of_property_read_bool(pdata->dev->of_node, "gpio-controller"))
> +		return 0;
> +
> +	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;
> +	ret = devm_gpiochip_add_data(pdata->dev, &pdata->gchip, pdata);
> +	if (ret)
> +		dev_err(pdata->dev, "can't add gpio chip\n");
> +
> +	return ret;
> +}
> +
>  static int ti_sn_bridge_probe(struct i2c_client *client,
>  			      const struct i2c_device_id *id)
>  {
> @@ -937,6 +1145,12 @@ static int ti_sn_bridge_probe(struct i2c_client *client,
>  
>  	pm_runtime_enable(pdata->dev);
>  
> +	ret = ti_sn_setup_gpio_controller(pdata);
> +	if (ret) {
> +		pm_runtime_disable(pdata->dev);
> +		return ret;
> +	}
> +
>  	i2c_set_clientdata(client, pdata);
>  
>  	pdata->aux.name = "ti-sn65dsi86-aux";
> -- 
> 2.26.2.645.ge9eca65c58-goog
> 

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