Re: [PATCH RESEND 4/4] drm: bridge: Generic GPIO mux driver

[Laurent Pinchart]

Hi Hsin-Yi and Nicolas,

Thank you for the patch.

On Wed, Dec 11, 2019 at 02:19:11PM +0800, Hsin-Yi Wang wrote:
> From: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> 
> This driver supports single input, 2 output display mux (e.g.
> HDMI mux), that provide its status via a GPIO.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> Signed-off-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/Kconfig            |  10 +
>  drivers/gpu/drm/bridge/Makefile           |   1 +
>  drivers/gpu/drm/bridge/generic-gpio-mux.c | 306 ++++++++++++++++++++++
>  3 files changed, 317 insertions(+)
>  create mode 100644 drivers/gpu/drm/bridge/generic-gpio-mux.c
> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index 1f3fc6bec842..4734f6993858 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -54,6 +54,16 @@ config DRM_DUMB_VGA_DAC
>  	  Support for non-programmable RGB to VGA DAC bridges, such as ADI
>  	  ADV7123, TI THS8134 and THS8135 or passive resistor ladder DACs.
>  
> +config DRM_GENERIC_GPIO_MUX
> +	tristate "Generic GPIO-controlled mux"
> +	depends on OF
> +	select DRM_KMS_HELPER
> +	---help---
> +	  This bridge driver models a GPIO-controlled display mux with one
> +	  input, 2 outputs (e.g. an HDMI mux). The hardware decides which output
> +	  is active, reports it as a GPIO, and the driver redirects calls to the
> +	  appropriate downstream bridge (if any).

My understanding of the issue was that the mux was controllable by a
GPIO, not that the GPIO would report its status. This changes a few
things. How is the mux controlled then ?

>  config DRM_LVDS_ENCODER
>  	tristate "Transparent parallel to LVDS encoder support"
>  	depends on OF
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 7a1e0ec032e6..1c0c92667ac4 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -3,6 +3,7 @@ obj-$(CONFIG_DRM_ANALOGIX_ANX7688) += analogix-anx7688.o
>  obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
>  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
>  obj-$(CONFIG_DRM_DUMB_VGA_DAC) += dumb-vga-dac.o
> +obj-$(CONFIG_DRM_GENERIC_GPIO_MUX) += generic-gpio-mux.o
>  obj-$(CONFIG_DRM_LVDS_ENCODER) += lvds-encoder.o
>  obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o
>  obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
> diff --git a/drivers/gpu/drm/bridge/generic-gpio-mux.c b/drivers/gpu/drm/bridge/generic-gpio-mux.c
> new file mode 100644
> index 000000000000..ba08321dcc17
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/generic-gpio-mux.c
> @@ -0,0 +1,306 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Generic gpio mux bridge driver
> + *
> + * Copyright 2016 Google LLC
> + */
> +
> +

One blank line is enough.

> +#include <linux/gpio.h>
> +#include <linux/interrupt.h>
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_gpio.h>
> +#include <linux/of_graph.h>

Could you please sort these headers alphabetically ?

> +#include <drm/drm_bridge.h>
> +#include <drm/drm_crtc_helper.h>
> +#include <drm/drm_probe_helper.h>
> +
> +struct gpio_display_mux {
> +	struct device *dev;
> +
> +	struct gpio_desc *gpiod_detect;
> +	int detect_irq;
> +
> +	struct drm_bridge bridge;
> +
> +	struct drm_bridge *next[2];
> +};
> +
> +static inline struct gpio_display_mux *bridge_to_gpio_display_mux(
> +		struct drm_bridge *bridge)
> +{
> +	return container_of(bridge, struct gpio_display_mux, bridge);
> +}
> +
> +static irqreturn_t gpio_display_mux_det_threaded_handler(int unused, void *data)
> +{
> +	struct gpio_display_mux *gpio_display_mux = data;

gpio_display_mux is a long variable name. You can shorten it to mux here
and below.

> +	int active = gpiod_get_value(gpio_display_mux->gpiod_detect);
> +
> +	dev_dbg(gpio_display_mux->dev, "Interrupt %d!\n", active);
> +
> +	if (gpio_display_mux->bridge.dev)
> +		drm_kms_helper_hotplug_event(gpio_display_mux->bridge.dev);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int gpio_display_mux_attach(struct drm_bridge *bridge)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +			bridge_to_gpio_display_mux(bridge);
> +	struct drm_bridge *next;
> +	int i;

i never takes negative values, you can make it an unsigned int.

> +
> +	for (i = 0; i < ARRAY_SIZE(gpio_display_mux->next); i++) {
> +		next = gpio_display_mux->next[i];
> +		if (next)
> +			next->encoder = bridge->encoder;
> +	}
> +
> +	return 0;
> +}
> +
> +static bool gpio_display_mux_mode_fixup(struct drm_bridge *bridge,
> +				const struct drm_display_mode *mode,
> +				struct drm_display_mode *adjusted_mode)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	int active;
> +	struct drm_bridge *next;
> +
> +	active = gpiod_get_value(gpio_display_mux->gpiod_detect);

What if the value of the GPIO changes between, let's say, this operation
and gpio_display_mux_mode_set() ? This doesn't seem very stable to me.
DRM/KMS hasn't been designed to have the output routing configured
externally without any control from the drivers.

> +	next = gpio_display_mux->next[active];

This will crash if gpiod_get_value() returns an error. Same for the
other functions below.

> +
> +	if (next && next->funcs->mode_fixup)
> +		return next->funcs->mode_fixup(next, mode, adjusted_mode);
> +	else
> +		return true;
> +}
> +
> +static void gpio_display_mux_mode_set(struct drm_bridge *bridge,
> +				struct drm_display_mode *mode,
> +				struct drm_display_mode *adjusted_mode)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	int active;
> +	struct drm_bridge *next;
> +
> +	active = gpiod_get_value(gpio_display_mux->gpiod_detect);
> +	next = gpio_display_mux->next[active];
> +
> +	if (next && next->funcs->mode_set)
> +		next->funcs->mode_set(next, mode, adjusted_mode);
> +}
> +
> +/**

This isn't kerneldoc, the comment should start with /*. Same comment
below.

> + * Since this driver _reacts_ to mux changes, we need to make sure all
> + * downstream bridges are pre-enabled.

I'm afraid the problem scope seems bigger than I initially anticipated
:-( We're in the hack territory here, and I think we need to search for
a proper solution. We need to start with a detailed description of the
hardware and the use cases.

> + */
> +static void gpio_display_mux_pre_enable(struct drm_bridge *bridge)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	struct drm_bridge *next;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(gpio_display_mux->next); i++) {
> +		next = gpio_display_mux->next[i];
> +		if (next && next->funcs->pre_enable)
> +			next->funcs->pre_enable(next);
> +	}
> +}
> +
> +static void gpio_display_mux_post_disable(struct drm_bridge *bridge)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	struct drm_bridge *next;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(gpio_display_mux->next); i++) {
> +		next = gpio_display_mux->next[i];
> +		if (next && next->funcs->post_disable)
> +			next->funcs->post_disable(next);
> +	}
> +}
> +
> +/**
> + * In an ideal mux driver, only the currently selected bridge should be enabled.
> + * For the sake of simplicity, we just just enable/disable all downstream
> + * bridges at the same time.
> + */
> +static void gpio_display_mux_enable(struct drm_bridge *bridge)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	struct drm_bridge *next;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(gpio_display_mux->next); i++) {
> +		next = gpio_display_mux->next[i];
> +		if (next && next->funcs->enable)
> +			next->funcs->enable(next);
> +	}
> +}
> +
> +static void gpio_display_mux_disable(struct drm_bridge *bridge)
> +{
> +	struct gpio_display_mux *gpio_display_mux =
> +		bridge_to_gpio_display_mux(bridge);
> +	struct drm_bridge *next;
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(gpio_display_mux->next); i++) {
> +		next = gpio_display_mux->next[i];
> +		if (next && next->funcs->disable)
> +			next->funcs->disable(next);
> +	}
> +}
> +
> +static const struct drm_bridge_funcs gpio_display_mux_bridge_funcs = {
> +	.attach = gpio_display_mux_attach,
> +	.mode_fixup = gpio_display_mux_mode_fixup,
> +	.disable = gpio_display_mux_disable,
> +	.post_disable = gpio_display_mux_post_disable,
> +	.mode_set = gpio_display_mux_mode_set,
> +	.pre_enable = gpio_display_mux_pre_enable,
> +	.enable = gpio_display_mux_enable,
> +};
> +
> +static int gpio_display_mux_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct gpio_display_mux *gpio_display_mux;
> +	struct device_node *port, *ep, *remote;
> +	int ret;
> +	u32 reg;
> +
> +	gpio_display_mux = devm_kzalloc(dev, sizeof(*gpio_display_mux),
> +					GFP_KERNEL);
> +	if (!gpio_display_mux)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, gpio_display_mux);
> +	gpio_display_mux->dev = &pdev->dev;
> +
> +	gpio_display_mux->bridge.of_node = dev->of_node;
> +
> +	gpio_display_mux->gpiod_detect =
> +		devm_gpiod_get(dev, "detect", GPIOD_IN);
> +	if (IS_ERR(gpio_display_mux->gpiod_detect))
> +		return PTR_ERR(gpio_display_mux->gpiod_detect);
> +
> +	gpio_display_mux->detect_irq =
> +		gpiod_to_irq(gpio_display_mux->gpiod_detect);
> +	if (gpio_display_mux->detect_irq < 0) {
> +		dev_err(dev, "Failed to get output irq %d\n",
> +			gpio_display_mux->detect_irq);
> +		return -ENODEV;
> +	}
> +
> +	port = of_graph_get_port_by_id(dev->of_node, 1);
> +	if (!port) {
> +		dev_err(dev, "Missing output port node\n");
> +		return -EINVAL;
> +	}
> +
> +	for_each_child_of_node(port, ep) {
> +		if (!ep->name || (of_node_cmp(ep->name, "endpoint") != 0)) {
> +			of_node_put(ep);
> +			continue;
> +		}
> +
> +		if (of_property_read_u32(ep, "reg", &reg) < 0 ||
> +				reg >= ARRAY_SIZE(gpio_display_mux->next)) {
> +			dev_err(dev,
> +			    "Missing/invalid reg property for endpoint %s\n",
> +				ep->full_name);
> +			of_node_put(ep);
> +			of_node_put(port);
> +			return -EINVAL;
> +		}
> +
> +		remote = of_graph_get_remote_port_parent(ep);
> +		if (!remote) {
> +			dev_err(dev,
> +			    "Missing connector/bridge node for endpoint %s\n",
> +				ep->full_name);
> +			of_node_put(ep);
> +			of_node_put(port);
> +			return -EINVAL;
> +		}
> +		of_node_put(ep);
> +
> +		if (of_device_is_compatible(remote, "hdmi-connector")) {
> +			of_node_put(remote);
> +			continue;
> +		}

This special case makes me think that something is wrong. I believe the
connector driver from
https://patchwork.freedesktop.org/patch/344477/?series=63328&rev=59
could help.

> +
> +		gpio_display_mux->next[reg] = of_drm_find_bridge(remote);

What if the connected device is a panel and not a bridge ?

> +		if (!gpio_display_mux->next[reg]) {
> +			dev_err(dev, "Waiting for external bridge %s\n",
> +				remote->name);
> +			of_node_put(remote);
> +			of_node_put(port);
> +			return -EPROBE_DEFER;
> +		}
> +
> +		of_node_put(remote);
> +	}
> +	of_node_put(port);
> +
> +	gpio_display_mux->bridge.funcs = &gpio_display_mux_bridge_funcs;
> +	drm_bridge_add(&gpio_display_mux->bridge);
> +
> +	ret = devm_request_threaded_irq(dev, gpio_display_mux->detect_irq,
> +				NULL,
> +				gpio_display_mux_det_threaded_handler,
> +				IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING |
> +					IRQF_ONESHOT,
> +				"gpio-display-mux-det", gpio_display_mux);
> +	if (ret) {
> +		dev_err(dev, "Failed to request MUX_DET threaded irq\n");
> +		goto err_bridge_remove;
> +	}
> +
> +	return 0;
> +
> +err_bridge_remove:
> +	drm_bridge_remove(&gpio_display_mux->bridge);
> +
> +	return ret;
> +}
> +
> +static int gpio_display_mux_remove(struct platform_device *pdev)
> +{
> +	struct gpio_display_mux *gpio_display_mux = platform_get_drvdata(pdev);
> +
> +	drm_bridge_remove(&gpio_display_mux->bridge);

If the GPIO IRQ is triggered here you'll have trouble. You need to
disable the IRQ, or free it, before removing the bridge.

> +
> +	return 0;
> +}
> +
> +static const struct of_device_id gpio_display_mux_match[] = {
> +	{ .compatible = "gpio-display-mux", },
> +	{},
> +};
> +
> +struct platform_driver gpio_display_mux_driver = {
> +	.probe = gpio_display_mux_probe,
> +	.remove = gpio_display_mux_remove,
> +	.driver = {
> +		.name = "gpio-display-mux",
> +		.of_match_table = gpio_display_mux_match,
> +	},
> +};
> +
> +module_platform_driver(gpio_display_mux_driver);
> +
> +MODULE_DESCRIPTION("GPIO-controlled display mux");
> +MODULE_AUTHOR("Nicolas Boichat <drinkcat@xxxxxxxxxxxx>");
> +MODULE_LICENSE("GPL v2");

-- 
Regards,

Laurent Pinchart