[PATCH v2] drm/panel: rpi-touchscreen: Add backlight support

[PATCH v2] drm/panel: rpi-touchscreen: Add backlight support

[Nicolas Saenz Julienne]

This patch exposes backlight control into userspace by creating a
backlight device instead of directly accessing the PWM registers.

The backlight driver can't go on a separate file as it shares the I2C
bus & address with the panel.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
v1 -> v2:
  - Add Kconfig dependency with BACKLIGHT_CLASS_DEVICE

 drivers/gpu/drm/panel/Kconfig                 |  1 +
 .../drm/panel/panel-raspberrypi-touchscreen.c | 33 +++++++++++++++++--
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
index 6020c30a33b3..1ce35483f342 100644
--- a/drivers/gpu/drm/panel/Kconfig
+++ b/drivers/gpu/drm/panel/Kconfig
@@ -112,6 +112,7 @@ config DRM_PANEL_PANASONIC_VVX10F034N00
 config DRM_PANEL_RASPBERRYPI_TOUCHSCREEN
 	tristate "Raspberry Pi 7-inch touchscreen panel"
 	depends on DRM_MIPI_DSI
+	depends on BACKLIGHT_CLASS_DEVICE
 	help
 	  Say Y here if you want to enable support for the Raspberry
 	  Pi 7" Touchscreen.  To compile this driver as a module,
diff --git a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
index 2c9c9722734f..838b5c8767bc 100644
--- a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
+++ b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
@@ -52,6 +52,7 @@
 #include <linux/of_device.h>
 #include <linux/of_graph.h>
 #include <linux/pm.h>
+#include <linux/backlight.h>
 
 #include <drm/drm_panel.h>
 #include <drm/drmP.h>
@@ -196,6 +197,7 @@ struct rpi_touchscreen {
 	struct drm_panel base;
 	struct mipi_dsi_device *dsi;
 	struct i2c_client *i2c;
+	struct backlight_device *backlight;
 };
 
 static const struct drm_display_mode rpi_touchscreen_modes[] = {
@@ -256,7 +258,8 @@ static int rpi_touchscreen_disable(struct drm_panel *panel)
 {
 	struct rpi_touchscreen *ts = panel_to_ts(panel);
 
-	rpi_touchscreen_i2c_write(ts, REG_PWM, 0);
+	ts->backlight->props.brightness = 0;
+	backlight_update_status(ts->backlight);
 
 	rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
 	udelay(1);
@@ -300,7 +303,8 @@ static int rpi_touchscreen_enable(struct drm_panel *panel)
 	msleep(100);
 
 	/* Turn on the backlight. */
-	rpi_touchscreen_i2c_write(ts, REG_PWM, 255);
+	ts->backlight->props.brightness = 255;
+	backlight_update_status(ts->backlight);
 
 	/* Default to the same orientation as the closed source
 	 * firmware used for the panel.  Runtime rotation
@@ -358,12 +362,26 @@ static const struct drm_panel_funcs rpi_touchscreen_funcs = {
 	.get_modes = rpi_touchscreen_get_modes,
 };
 
+static int raspberrypi_bl_update_status(struct backlight_device *bl)
+{
+	struct rpi_touchscreen *ts = bl_get_data(bl);
+
+	rpi_touchscreen_i2c_write(ts, REG_PWM, bl->props.brightness);
+
+	return 0;
+}
+
+static const struct backlight_ops raspberrypi_bl_ops = {
+	.update_status = raspberrypi_bl_update_status,
+};
+
 static int rpi_touchscreen_probe(struct i2c_client *i2c,
 				 const struct i2c_device_id *id)
 {
 	struct device *dev = &i2c->dev;
 	struct rpi_touchscreen *ts;
 	struct device_node *endpoint, *dsi_host_node;
+	struct backlight_properties props;
 	struct mipi_dsi_host *host;
 	int ret, ver;
 	struct mipi_dsi_device_info info = {
@@ -398,6 +416,17 @@ static int rpi_touchscreen_probe(struct i2c_client *i2c,
 	/* Turn off at boot, so we can cleanly sequence powering on. */
 	rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
 
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 255;
+	ts->backlight = devm_backlight_device_register(dev, dev_name(dev), dev,
+						       ts, &raspberrypi_bl_ops,
+						       &props);
+	if (IS_ERR(ts->backlight)) {
+		dev_err(dev, "Failed to create backlight device\n");
+		return PTR_ERR(ts->backlight);
+	}
+
 	/* Look up the DSI host.  It needs to probe before we do. */
 	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
 	dsi_host_node = of_graph_get_remote_port_parent(endpoint);
-- 
2.19.2

Re: [PATCH v2] drm/panel: rpi-touchscreen: Add backlight support

[Eric Anholt]

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Nicolas Saenz Julienne <nsaenzjulienne@suse.de> writes:

> This patch exposes backlight control into userspace by creating a
> backlight device instead of directly accessing the PWM registers.
>
> The backlight driver can't go on a separate file as it shares the I2C
> bus & address with the panel.

I remember some concerns from Gordon about exposing the backlight PWM.
Gordon, care to chime in on this?

> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
> v1 -> v2:
>   - Add Kconfig dependency with BACKLIGHT_CLASS_DEVICE
>
>  drivers/gpu/drm/panel/Kconfig                 |  1 +
>  .../drm/panel/panel-raspberrypi-touchscreen.c | 33 +++++++++++++++++--
>  2 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
> index 6020c30a33b3..1ce35483f342 100644
> --- a/drivers/gpu/drm/panel/Kconfig
> +++ b/drivers/gpu/drm/panel/Kconfig
> @@ -112,6 +112,7 @@ config DRM_PANEL_PANASONIC_VVX10F034N00
>  config DRM_PANEL_RASPBERRYPI_TOUCHSCREEN
>  	tristate "Raspberry Pi 7-inch touchscreen panel"
>  	depends on DRM_MIPI_DSI
> +	depends on BACKLIGHT_CLASS_DEVICE
>  	help
>  	  Say Y here if you want to enable support for the Raspberry
>  	  Pi 7" Touchscreen.  To compile this driver as a module,
> diff --git a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
> index 2c9c9722734f..838b5c8767bc 100644
> --- a/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
> +++ b/drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c
> @@ -52,6 +52,7 @@
>  #include <linux/of_device.h>
>  #include <linux/of_graph.h>
>  #include <linux/pm.h>
> +#include <linux/backlight.h>
>  
>  #include <drm/drm_panel.h>
>  #include <drm/drmP.h>
> @@ -196,6 +197,7 @@ struct rpi_touchscreen {
>  	struct drm_panel base;
>  	struct mipi_dsi_device *dsi;
>  	struct i2c_client *i2c;
> +	struct backlight_device *backlight;
>  };
>  
>  static const struct drm_display_mode rpi_touchscreen_modes[] = {
> @@ -256,7 +258,8 @@ static int rpi_touchscreen_disable(struct drm_panel *panel)
>  {
>  	struct rpi_touchscreen *ts = panel_to_ts(panel);
>  
> -	rpi_touchscreen_i2c_write(ts, REG_PWM, 0);
> +	ts->backlight->props.brightness = 0;
> +	backlight_update_status(ts->backlight);
>  
>  	rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
>  	udelay(1);
> @@ -300,7 +303,8 @@ static int rpi_touchscreen_enable(struct drm_panel *panel)
>  	msleep(100);
>  
>  	/* Turn on the backlight. */
> -	rpi_touchscreen_i2c_write(ts, REG_PWM, 255);
> +	ts->backlight->props.brightness = 255;
> +	backlight_update_status(ts->backlight);
>  
>  	/* Default to the same orientation as the closed source
>  	 * firmware used for the panel.  Runtime rotation
> @@ -358,12 +362,26 @@ static const struct drm_panel_funcs rpi_touchscreen_funcs = {
>  	.get_modes = rpi_touchscreen_get_modes,
>  };
>  
> +static int raspberrypi_bl_update_status(struct backlight_device *bl)
> +{
> +	struct rpi_touchscreen *ts = bl_get_data(bl);
> +
> +	rpi_touchscreen_i2c_write(ts, REG_PWM, bl->props.brightness);
> +
> +	return 0;
> +}
> +
> +static const struct backlight_ops raspberrypi_bl_ops = {
> +	.update_status = raspberrypi_bl_update_status,
> +};
> +
>  static int rpi_touchscreen_probe(struct i2c_client *i2c,
>  				 const struct i2c_device_id *id)
>  {
>  	struct device *dev = &i2c->dev;
>  	struct rpi_touchscreen *ts;
>  	struct device_node *endpoint, *dsi_host_node;
> +	struct backlight_properties props;
>  	struct mipi_dsi_host *host;
>  	int ret, ver;
>  	struct mipi_dsi_device_info info = {
> @@ -398,6 +416,17 @@ static int rpi_touchscreen_probe(struct i2c_client *i2c,
>  	/* Turn off at boot, so we can cleanly sequence powering on. */
>  	rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
>  
> +	memset(&props, 0, sizeof(props));
> +	props.type = BACKLIGHT_RAW;
> +	props.max_brightness = 255;
> +	ts->backlight = devm_backlight_device_register(dev, dev_name(dev), dev,
> +						       ts, &raspberrypi_bl_ops,
> +						       &props);
> +	if (IS_ERR(ts->backlight)) {
> +		dev_err(dev, "Failed to create backlight device\n");
> +		return PTR_ERR(ts->backlight);
> +	}
> +
>  	/* Look up the DSI host.  It needs to probe before we do. */
>  	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
>  	dsi_host_node = of_graph_get_remote_port_parent(endpoint);
> -- 
> 2.19.2

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Re: [PATCH v2] drm/panel: rpi-touchscreen: Add backlight support

[Nicolas Saenz Julienne]

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On Thu, 2018-12-20 at 18:36 +0000, Gordon Hollingworth wrote:
> Assuming this is using the firmware interface then yes it's fine.  If
> it is using the i2c directly then it's possible to clash with the GPU
> driving the camera

Well we're already in such a situation without this patch, as the panel
enables the back-light though the I2C lines. This is only enabled by an
overlay, it's left to the user's discretion.

As commented previously by Alex Graf and given the constraints, I think
that it would make sense to start considering both options as good
(using FW & direct I2C access). We are defaulting to the FW based one,
but providing support/overlays for the direct access doesn't seem a bad
compromise to me.

I do understand Gordon's concerns. Maybe it would be nice for the
firmware to detect device tree nodes accessing I2C0 and disable the
camera. Or providing a FW configuration option.

Kind regards,
Nicolas

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