Re: [RFC PATCH 3/4] drm: bridge: Generic GPIO mux driver

[Nicolas Boichat]

(whoops, apologies for the CHROMIUM tag in the subject line...)

On Tue, Jun 28, 2016 at 4:52 PM, Archit Taneja <architt@xxxxxxxxxxxxxx> wrote:
>
>
> On 06/27/2016 01:18 PM, Nicolas Boichat wrote:
>>
>> This driver supports single input, 2 output display mux (e.g.
>> HDMI mux), that provides its status via a GPIO.
>
>
> This might not work if we had a 2 or more bridges connected
> one after the other at the output ports. It would be nicer
> if the interrupt handler directly modified the drm_bridge's
> next pointer rather than managing things by its own.

I don't think we can directly change ->next as different functions
need different handling. For example, pre_enable should be called on
all possible downstream bridges, as we cannot know in advance which
bridge should be ready. So does attach, but I think that's easier to
solve.

> That being said, the bridge chains (by setting the next
> pointers) aren't expected to change after they are set up.
> In order to use make this a truly generic driver, we'd
> probably need to add some sort of locking for the entire
> bridge chain to make sure we don't change things in the
> middle of a modeset. We don't really need to add this
> functionality unless there are many more platforms like
> these have non-static muxes in the display chain.

Agree with that. Also, since our downstream bridges (HDMI connector,
so no bridge, and anx7688) don't have enable/disable callbacks, we are
actually using a simpler version of this driver that just leaves all
downstream bridges enabled.

> It would be better if this driver was considered to be
> used only for the mux hardware that's used on the board.
>
> Archit
>
>
>>
>> Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
>> ---
>>   drivers/gpu/drm/bridge/Kconfig            |  11 +
>>   drivers/gpu/drm/bridge/Makefile           |   1 +
>>   drivers/gpu/drm/bridge/generic-gpio-mux.c | 347
>> ++++++++++++++++++++++++++++++
>>   3 files changed, 359 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 da489f0..f1f6fc6 100644
>> --- a/drivers/gpu/drm/bridge/Kconfig
>> +++ b/drivers/gpu/drm/bridge/Kconfig
>> @@ -41,6 +41,17 @@ config DRM_DW_HDMI_AHB_AUDIO
>>           Designware HDMI block.  This is used in conjunction with
>>           the i.MX6 HDMI driver.
>>
>> +config DRM_GENERIC_GPIO_MUX
>> +       tristate "Generic GPIO-controlled mux"
>> +       depends on DRM
>> +       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).
>> +
>>   config DRM_NXP_PTN3460
>>         tristate "NXP PTN3460 DP/LVDS bridge"
>>         depends on OF
>> diff --git a/drivers/gpu/drm/bridge/Makefile
>> b/drivers/gpu/drm/bridge/Makefile
>> index 4846465..cb97274fd 100644
>> --- a/drivers/gpu/drm/bridge/Makefile
>> +++ b/drivers/gpu/drm/bridge/Makefile
>> @@ -4,6 +4,7 @@ obj-$(CONFIG_DRM_ANALOGIX_ANX7688) += analogix-anx7688.o
>>   obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
>>   obj-$(CONFIG_DRM_DW_HDMI) += dw-hdmi.o
>>   obj-$(CONFIG_DRM_DW_HDMI_AHB_AUDIO) += dw-hdmi-ahb-audio.o
>> +obj-$(CONFIG_DRM_GENERIC_GPIO_MUX) += generic-gpio-mux.o
>>   obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
>>   obj-$(CONFIG_DRM_PARADE_PS8622) += parade-ps8622.o
>>   obj-$(CONFIG_DRM_SII902X) += sii902x.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 0000000..d3367e2
>> --- /dev/null
>> +++ b/drivers/gpu/drm/bridge/generic-gpio-mux.c
>> @@ -0,0 +1,347 @@
>> +/*
>> + * ANX7688 HDMI->DP bridge driver
>> + *
>> + * Copyright (C) 2016 Google, Inc.
>> + *
>> + * This software is licensed under the terms of the GNU General Public
>> + * License version 2, as published by the Free Software Foundation, and
>> + * may be copied, distributed, and modified under those terms.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>> + * GNU General Public License for more details.
>> + */
>> +
>> +#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>
>> +#include <drm/drm_crtc.h>
>> +#include <drm/drm_crtc_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];
>> +
>> +       struct mutex lock;
>> +       int active;
>> +       bool enabled;
>> +};
>> +
>> +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;
>> +       struct drm_bridge *next;
>> +       int active;
>> +
>> +       active = gpiod_get_value(gpio_display_mux->gpiod_detect);
>> +
>> +       dev_dbg(gpio_display_mux->dev, "Interrupt %d!\n", active);
>> +
>> +       if (active == gpio_display_mux->active)
>> +               return IRQ_HANDLED;
>> +
>> +       /* Disable previous bridge */
>> +       mutex_lock(&gpio_display_mux->lock);
>> +       if (gpio_display_mux->enabled) {
>> +               next = gpio_display_mux->next[gpio_display_mux->active];
>> +               if (next && next->funcs->disable)
>> +                       next->funcs->disable(next);
>> +       }
>> +       mutex_unlock(&gpio_display_mux->lock);
>> +
>> +       if (gpio_display_mux->bridge.dev)
>> +
>> drm_kms_helper_hotplug_event(gpio_display_mux->bridge.dev);
>> +
>> +       /* Enable current bridge */
>> +       mutex_lock(&gpio_display_mux->lock);
>> +       if (gpio_display_mux->enabled) {
>> +               next = gpio_display_mux->next[active];
>> +               if (next && next->funcs->enable)
>> +                       next->funcs->enable(next);
>> +       }
>> +       gpio_display_mux->active = active;
>> +       mutex_unlock(&gpio_display_mux->lock);
>> +
>> +       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;
>> +
>> +       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);
>> +       struct drm_bridge *next;
>> +
>> +       next = gpio_display_mux->next[gpio_display_mux->active];
>> +
>> +       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);
>> +       struct drm_bridge *next;
>> +
>> +       next = gpio_display_mux->next[gpio_display_mux->active];
>> +
>> +       if (next && next->funcs->mode_set)
>> +               next->funcs->mode_set(next, mode, adjusted_mode);
>> +}
>> +
>> +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;
>> +
>> +       mutex_lock(&gpio_display_mux->lock);
>> +
>> +       next = gpio_display_mux->next[gpio_display_mux->active];
>> +       if (next && next->funcs->enable)
>> +               next->funcs->enable(next);
>> +
>> +       gpio_display_mux->enabled = true;
>> +
>> +       mutex_unlock(&gpio_display_mux->lock);
>> +}
>> +
>> +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;
>> +
>> +       mutex_lock(&gpio_display_mux->lock);
>> +
>> +       next = gpio_display_mux->next[gpio_display_mux->active];
>> +       if (next && next->funcs->disable)
>> +               next->funcs->disable(next);
>> +
>> +       gpio_display_mux->enabled = false;
>> +
>> +       mutex_unlock(&gpio_display_mux->lock);
>> +}
>> +
>> +/**
>> + * Since this driver _reacts_ to mux changes, we need to make sure all
>> + * downstream bridges are pre-enabled.
>> + */
>> +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);
>> +       }
>> +}
>> +
>> +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;
>> +
>> +       mutex_init(&gpio_display_mux->lock);
>> +
>> +       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;
>> +               }
>> +
>> +               gpio_display_mux->next[reg] = of_drm_find_bridge(remote);
>> +               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;
>> +       ret = drm_bridge_add(&gpio_display_mux->bridge);
>> +       if (ret < 0) {
>> +               dev_err(dev, "Failed to add drm bridge\n");
>> +               return ret;
>> +       }
>> +
>> +       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;
>> +       }
>> +
>> +       gpio_display_mux->active =
>> +                       gpiod_get_value(gpio_display_mux->gpiod_detect);
>> +
>> +       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);
>> +
>> +       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");
>>
>
> --
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