Re: [v3 2/2] backlight: Add DisplayPort aux backlight driver

[rajeevny@codeaurora.org]

On 26-04-2021 15:19, Jani Nikula wrote:
> On Mon, 26 Apr 2021, Rajeev Nandan <rajeevny@codeaurora.org> wrote:
>> Add backlight driver for the panels supporting backlight control
>> using DPCD registers on the DisplayPort aux channel.
> 
> No, please don't do this.
> 
> I wrote you last week in reply to v1 why I thought merging this would
> not be a good idea [1]. Why have you sent two versions since then
> without replying to me, or Cc'ing me or Lyude?
> 
> I think it's an even worse idea to merge this to
> drivers/video/backlight. With DP AUX backlight you can't pretend it's
> just an independent aux interface for backlight without everything else
> around it. It's not independent of eDP, and exposing it as a direct
> backlight sysfs interface bypasses the encoder.
> 
> And it still remains that there is existing DP AUX backlight code in
> use, in the tree, with more features than this, with plans and
> previously submitted patches to lift from one driver to drm core, and
> with patches to add support to another driver.
> 
> I don't say this lightly, or very often at all, but,
> 
> NAK.
> 
> 
> BR,
> Jani.
> 
> 
> [1] https://lore.kernel.org/dri-devel/871rb5bcf9.fsf@intel.com/
> 

Hi Jani,

Apologies for not acknowledging your comment on v1.
I was looking here [1] for all the comments I would be receiving on
my patches. I was not aware that the comments on the cover letter don't
appear on this page. Also, I completely missed your mail.
I will ensure such omissions don't happen again.

Keeping your comments in mind, I will look into Lyude's series and
work upon my code.

[1] https://patchwork.freedesktop.org/series/89085/

Yours sincerely,
Rajeev


>> 
>> Changes in v2:
>> - New (most of the code reused from drm_dp_aux_backlight.c of v1)
>> 
>> Changes in v3:
>> - Add missing ';' to fix module compilation (kernel test bot)
>> 
>> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
>> ---
>>  drivers/video/backlight/Kconfig            |   7 +
>>  drivers/video/backlight/Makefile           |   1 +
>>  drivers/video/backlight/dp_aux_backlight.c | 245 
>> +++++++++++++++++++++++++++++
>>  3 files changed, 253 insertions(+)
>>  create mode 100644 drivers/video/backlight/dp_aux_backlight.c
>> 
>> diff --git a/drivers/video/backlight/Kconfig 
>> b/drivers/video/backlight/Kconfig
>> index d83c87b..82c88f0 100644
>> --- a/drivers/video/backlight/Kconfig
>> +++ b/drivers/video/backlight/Kconfig
>> @@ -456,6 +456,13 @@ config BACKLIGHT_LED
>>  	  If you have a LCD backlight adjustable by LED class driver, say Y
>>  	  to enable this driver.
>> 
>> +config BACKLIGHT_DP_AUX
>> +       tristate "DisplayPort aux backlight driver"
>> +       depends on DRM && DRM_KMS_HELPER
>> +       help
>> +         If you have a panel backlight controlled by DPCD registers
>> +         on the DisplayPort aux channel, say Y to enable this driver.
>> +
>>  endif # BACKLIGHT_CLASS_DEVICE
>> 
>>  endmenu
>> diff --git a/drivers/video/backlight/Makefile 
>> b/drivers/video/backlight/Makefile
>> index 685f3f1..ba23c7c 100644
>> --- a/drivers/video/backlight/Makefile
>> +++ b/drivers/video/backlight/Makefile
>> @@ -57,3 +57,4 @@ obj-$(CONFIG_BACKLIGHT_WM831X)		+= wm831x_bl.o
>>  obj-$(CONFIG_BACKLIGHT_ARCXCNN) 	+= arcxcnn_bl.o
>>  obj-$(CONFIG_BACKLIGHT_RAVE_SP)		+= rave-sp-backlight.o
>>  obj-$(CONFIG_BACKLIGHT_LED)		+= led_bl.o
>> +obj-$(CONFIG_BACKLIGHT_DP_AUX)		+= dp_aux_backlight.o
>> diff --git a/drivers/video/backlight/dp_aux_backlight.c 
>> b/drivers/video/backlight/dp_aux_backlight.c
>> new file mode 100644
>> index 00000000..3398383
>> --- /dev/null
>> +++ b/drivers/video/backlight/dp_aux_backlight.c
>> @@ -0,0 +1,245 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Backlight driver to control the brightness over DisplayPort aux 
>> channel.
>> + */
>> +
>> +#include <linux/backlight.h>
>> +#include <linux/err.h>
>> +#include <linux/gpio/consumer.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <drm/drm_dp_helper.h>
>> +
>> +#define DP_AUX_MAX_BRIGHTNESS		0xffff
>> +
>> +/**
>> + * struct dp_aux_backlight - DisplayPort aux backlight data
>> + * @dev: pointer to our device.
>> + * @aux: the DisplayPort aux channel.
>> + * @enable_gpio: the backlight enable gpio.
>> + * @enabled: true if backlight is enabled else false.
>> + */
>> +struct dp_aux_backlight {
>> +	struct device *dev;
>> +	struct drm_dp_aux *aux;
>> +	struct gpio_desc *enable_gpio;
>> +	bool enabled;
>> +};
>> +
>> +static struct drm_dp_aux *i2c_to_aux(struct i2c_adapter *i2c)
>> +{
>> +	return container_of(i2c, struct drm_dp_aux, ddc);
>> +}
>> +
>> +static int dp_aux_backlight_enable(struct dp_aux_backlight *aux_bl)
>> +{
>> +	u8 val = 0;
>> +	int ret;
>> +
>> +	if (aux_bl->enabled)
>> +		return 0;
>> +
>> +	/* Set backlight control mode */
>> +	ret = drm_dp_dpcd_readb(aux_bl->aux, 
>> DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
>> +				&val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	val &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
>> +	val |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
>> +	ret = drm_dp_dpcd_writeb(aux_bl->aux, 
>> DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
>> +				 val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* Enable backlight */
>> +	ret = drm_dp_dpcd_readb(aux_bl->aux, 
>> DP_EDP_DISPLAY_CONTROL_REGISTER,
>> +				&val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	val |= DP_EDP_BACKLIGHT_ENABLE;
>> +	ret = drm_dp_dpcd_writeb(aux_bl->aux, 
>> DP_EDP_DISPLAY_CONTROL_REGISTER,
>> +				 val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	if (aux_bl->enable_gpio)
>> +		gpiod_set_value(aux_bl->enable_gpio, 1);
>> +
>> +	aux_bl->enabled = true;
>> +
>> +	return 0;
>> +}
>> +
>> +static int dp_aux_backlight_disable(struct dp_aux_backlight *aux_bl)
>> +{
>> +	u8 val = 0;
>> +	int ret;
>> +
>> +	if (!aux_bl->enabled)
>> +		return 0;
>> +
>> +	if (aux_bl->enable_gpio)
>> +		gpiod_set_value(aux_bl->enable_gpio, 0);
>> +
>> +	ret = drm_dp_dpcd_readb(aux_bl->aux, 
>> DP_EDP_DISPLAY_CONTROL_REGISTER,
>> +				&val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	val &= ~DP_EDP_BACKLIGHT_ENABLE;
>> +	ret = drm_dp_dpcd_writeb(aux_bl->aux, 
>> DP_EDP_DISPLAY_CONTROL_REGISTER,
>> +				 val);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	aux_bl->enabled = false;
>> +
>> +	return 0;
>> +}
>> +
>> +static int dp_aux_backlight_update_status(struct backlight_device 
>> *bd)
>> +{
>> +	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
>> +	u16 brightness = backlight_get_brightness(bd);
>> +	u8 val[2] = { 0x0 };
>> +	int ret = 0;
>> +
>> +	if (brightness > 0) {
>> +		val[0] = brightness >> 8;
>> +		val[1] = brightness & 0xff;
>> +		ret = drm_dp_dpcd_write(aux_bl->aux, 
>> DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
>> +					val, sizeof(val));
>> +		if (ret < 0)
>> +			return ret;
>> +
>> +		dp_aux_backlight_enable(aux_bl);
>> +	} else {
>> +		dp_aux_backlight_disable(aux_bl);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int dp_aux_backlight_get_brightness(struct backlight_device 
>> *bd)
>> +{
>> +	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
>> +	u8 val[2] = { 0x0 };
>> +	int ret = 0;
>> +
>> +	if (backlight_is_blank(bd))
>> +		return 0;
>> +
>> +	ret = drm_dp_dpcd_read(aux_bl->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
>> +			       &val, sizeof(val));
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	return (val[0] << 8 | val[1]);
>> +}
>> +
>> +static const struct backlight_ops aux_bl_ops = {
>> +	.update_status = dp_aux_backlight_update_status,
>> +	.get_brightness = dp_aux_backlight_get_brightness,
>> +};
>> +
>> +
>> +static int dp_aux_backlight_probe(struct platform_device *pdev)
>> +{
>> +	struct dp_aux_backlight *aux_bl;
>> +	struct backlight_device *bd;
>> +	struct backlight_properties bl_props = { 0 };
>> +	struct device_node *np;
>> +	struct i2c_adapter *ddc;
>> +	int ret = 0;
>> +	u32 val;
>> +
>> +	aux_bl = devm_kzalloc(&pdev->dev, sizeof(*aux_bl), GFP_KERNEL);
>> +	if (!aux_bl)
>> +		return -ENOMEM;
>> +
>> +	aux_bl->dev = &pdev->dev;
>> +
>> +	np = of_parse_phandle(pdev->dev.of_node, "ddc-i2c-bus", 0);
>> +	if (!np) {
>> +		dev_err(&pdev->dev, "failed to get aux ddc I2C bus\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	ddc = of_find_i2c_adapter_by_node(np);
>> +	of_node_put(np);
>> +	if (!ddc)
>> +		return -EPROBE_DEFER;
>> +
>> +	aux_bl->aux = i2c_to_aux(ddc);
>> +	dev_dbg(&pdev->dev, "using dp aux %s\n", aux_bl->aux->name);
>> +
>> +	aux_bl->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
>> +					     GPIOD_OUT_LOW);
>> +	if (IS_ERR(aux_bl->enable_gpio)) {
>> +		ret = PTR_ERR(aux_bl->enable_gpio);
>> +		goto free_ddc;
>> +	}
>> +
>> +	val = DP_AUX_MAX_BRIGHTNESS;
>> +	of_property_read_u32(pdev->dev.of_node, "max-brightness", &val);
>> +	if (val > DP_AUX_MAX_BRIGHTNESS)
>> +		val = DP_AUX_MAX_BRIGHTNESS;
>> +
>> +	bl_props.max_brightness = val;
>> +	bl_props.brightness = val;
>> +	bl_props.type = BACKLIGHT_RAW;
>> +	bd = devm_backlight_device_register(&pdev->dev, 
>> dev_name(&pdev->dev),
>> +					    &pdev->dev, aux_bl,
>> +					    &aux_bl_ops, &bl_props);
>> +	if (IS_ERR(bd)) {
>> +		ret = PTR_ERR(bd);
>> +		dev_err(&pdev->dev,
>> +			      "failed to register backlight (%d)\n", ret);
>> +		goto free_ddc;
>> +	}
>> +
>> +	platform_set_drvdata(pdev, bd);
>> +
>> +	return 0;
>> +
>> +free_ddc:
>> +	if (ddc)
>> +		put_device(&ddc->dev);
>> +
>> +	return ret;
>> +}
>> +
>> +static int dp_aux_backlight_remove(struct platform_device *pdev)
>> +{
>> +	struct backlight_device *bd = platform_get_drvdata(pdev);
>> +	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
>> +	struct i2c_adapter *ddc = &aux_bl->aux->ddc;
>> +
>> +	if (ddc)
>> +		put_device(&ddc->dev);
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct of_device_id dp_aux_bl_of_match_table[] = {
>> +	{ .compatible = "dp-aux-backlight"},
>> +	{},
>> +};
>> +MODULE_DEVICE_TABLE(of, dp_aux_bl_of_match_table);
>> +
>> +static struct platform_driver dp_aux_backlight_driver = {
>> +	.driver = {
>> +		.name = "dp-aux-backlight",
>> +		.of_match_table = dp_aux_bl_of_match_table,
>> +	},
>> +	.probe = dp_aux_backlight_probe,
>> +	.remove = dp_aux_backlight_remove,
>> +
>> +};
>> +module_platform_driver(dp_aux_backlight_driver);
>> +
>> +MODULE_DESCRIPTION("DisplayPort aux backlight driver");
>> +MODULE_LICENSE("GPL v2");