Message-ID: <7f8562df-7e1f-dcfb-1c58-f1edd9dcc606@suse.de>
Date:   Mon, 12 Jul 2021 11:41:34 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Rajeev Nandan <rajeevny@...eaurora.org>,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, thierry.reding@...il.com,
        sam@...nborg.org, robdclark@...il.com, dianders@...omium.org,
        lyude@...hat.com, jani.nikula@...el.com, robh@...nel.org,
        laurent.pinchart@...asonboard.com, a.hajda@...sung.com,
        daniel.thompson@...aro.org, hoegsberg@...omium.org,
        abhinavk@...eaurora.org, seanpaul@...omium.org,
        kalyan_t@...eaurora.org, mkrishn@...eaurora.org,
        lee.jones@...aro.org, jingoohan1@...il.com,
        linux-fbdev@...r.kernel.org
Subject: Re: [v8 1/6] drm/panel: add basic DP AUX backlight support



Am 26.06.21 um 18:51 schrieb Rajeev Nandan:
> Some panels support backlight control over DP AUX channel using
> VESA's standard backlight control interface.
> Using new DRM eDP backlight helpers, add support to create and
> register a backlight for those panels in drm_panel to simplify
> the panel drivers.
> 
> The panel driver with access to "struct drm_dp_aux" can create and
> register a backlight device using following code snippet in its
> probe() function:
> 
> 	err = drm_panel_dp_aux_backlight(panel, aux);
> 	if (err)
> 		return err;
> 
> Then drm_panel will handle backlight_(enable|disable) calls
> similar to the case when drm_panel_of_backlight() is used.
> 
> Currently, we are not supporting one feature where the source
> device can combine the backlight brightness levels set through
> DP AUX and the BL_PWM_DIM eDP connector pin. Since it's not
> required for the basic backlight controls, it can be added later.
> 
> Signed-off-by: Rajeev Nandan <rajeevny@...eaurora.org>
> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> Reviewed-by: Lyude Paul <lyude@...hat.com>
> ---
> 
> Changes in v5:
> - New
> 
> Changes in v6:
> - Fixed ordering of memory allocation (Douglas)
> - Updated word wrapping in a comment (Douglas)
> 
> Changes in v8:
> - Now using backlight_is_blank() to get the backlight blank status (Sam Ravnborg)
> 
>   drivers/gpu/drm/drm_panel.c | 108 ++++++++++++++++++++++++++++++++++++++++++++
>   include/drm/drm_panel.h     |  15 ++++--
>   2 files changed, 119 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index f634371..4fa1e3b 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -26,12 +26,20 @@
>   #include <linux/module.h>
>   
>   #include <drm/drm_crtc.h>
> +#include <drm/drm_dp_helper.h>
>   #include <drm/drm_panel.h>
>   #include <drm/drm_print.h>
>   
>   static DEFINE_MUTEX(panel_lock);
>   static LIST_HEAD(panel_list);
>   
> +struct dp_aux_backlight {
> +	struct backlight_device *base;
> +	struct drm_dp_aux *aux;
> +	struct drm_edp_backlight_info info;
> +	bool enabled;
> +};
> +
>   /**
>    * DOC: drm panel
>    *
> @@ -342,6 +350,106 @@ int drm_panel_of_backlight(struct drm_panel *panel)
>   	return 0;
>   }
>   EXPORT_SYMBOL(drm_panel_of_backlight);
> +
> +static int dp_aux_backlight_update_status(struct backlight_device *bd)
> +{
> +	struct dp_aux_backlight *bl = bl_get_data(bd);
> +	u16 brightness = backlight_get_brightness(bd);
> +	int ret = 0;
> +
> +	if (!backlight_is_blank(bd)) {
> +		if (!bl->enabled) {
> +			drm_edp_backlight_enable(bl->aux, &bl->info, brightness);
> +			bl->enabled = true;
> +			return 0;
> +		}
> +		ret = drm_edp_backlight_set_level(bl->aux, &bl->info, brightness);
> +	} else {
> +		if (bl->enabled) {
> +			drm_edp_backlight_disable(bl->aux, &bl->info);
> +			bl->enabled = false;
> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct backlight_ops dp_aux_bl_ops = {
> +	.update_status = dp_aux_backlight_update_status,
> +};
> +
> +/**
> + * drm_panel_dp_aux_backlight - create and use DP AUX backlight
> + * @panel: DRM panel
> + * @aux: The DP AUX channel to use
> + *
> + * Use this function to create and handle backlight if your panel
> + * supports backlight control over DP AUX channel using DPCD
> + * registers as per VESA's standard backlight control interface.
> + *
> + * When the panel is enabled backlight will be enabled after a
> + * successful call to &drm_panel_funcs.enable()
> + *
> + * When the panel is disabled backlight will be disabled before the
> + * call to &drm_panel_funcs.disable().
> + *
> + * A typical implementation for a panel driver supporting backlight
> + * control over DP AUX will call this function at probe time.
> + * Backlight will then be handled transparently without requiring
> + * any intervention from the driver.
> + *
> + * drm_panel_dp_aux_backlight() must be called after the call to drm_panel_init().
> + *
> + * Return: 0 on success or a negative error code on failure.
> + */
> +int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux)
> +{
> +	struct dp_aux_backlight *bl;
> +	struct backlight_properties props = { 0 };
> +	u16 current_level;
> +	u8 current_mode;
> +	u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
> +	int ret;
> +
> +	if (!panel || !panel->dev || !aux)
> +		return -EINVAL;
> +
> +	ret = drm_dp_dpcd_read(aux, DP_EDP_DPCD_REV, edp_dpcd,
> +			       EDP_DISPLAY_CTL_CAP_SIZE);

This creates a cyclic dependency between drm_kms_helper-ko and drm.ko. 
drm_panel.c is in the latter, while drm_dp_dpcd_read() in 
drm_dp_helper.c is in the former. Please fix.

Best regards
Thomas

> +	if (ret < 0)
> +		return ret;
> +
> +	if (!drm_edp_backlight_supported(edp_dpcd)) {
> +		DRM_DEV_INFO(panel->dev, "DP AUX backlight is not supported\n");
> +		return 0;
> +	}
> +
> +	bl = devm_kzalloc(panel->dev, sizeof(*bl), GFP_KERNEL);
> +	if (!bl)
> +		return -ENOMEM;
> +
> +	bl->aux = aux;
> +
> +	ret = drm_edp_backlight_init(aux, &bl->info, 0, edp_dpcd,
> +				     &current_level, &current_mode);
> +	if (ret < 0)
> +		return ret;
> +
> +	props.type = BACKLIGHT_RAW;
> +	props.brightness = current_level;
> +	props.max_brightness = bl->info.max;
> +
> +	bl->base = devm_backlight_device_register(panel->dev, "dp_aux_backlight",
> +						  panel->dev, bl,
> +						  &dp_aux_bl_ops, &props);
> +	if (IS_ERR(bl->base))
> +		return PTR_ERR(bl->base);
> +
> +	panel->backlight = bl->base;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
>   #endif
>   
>   MODULE_AUTHOR("Thierry Reding <treding@...dia.com>");
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 33605c3..3ebfaa6 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -32,6 +32,7 @@ struct backlight_device;
>   struct device_node;
>   struct drm_connector;
>   struct drm_device;
> +struct drm_dp_aux;
>   struct drm_panel;
>   struct display_timing;
>   
> @@ -64,8 +65,8 @@ enum drm_panel_orientation;
>    * the panel. This is the job of the .unprepare() function.
>    *
>    * Backlight can be handled automatically if configured using
> - * drm_panel_of_backlight(). Then the driver does not need to implement the
> - * functionality to enable/disable backlight.
> + * drm_panel_of_backlight() or drm_panel_dp_aux_backlight(). Then the driver
> + * does not need to implement the functionality to enable/disable backlight.
>    */
>   struct drm_panel_funcs {
>   	/**
> @@ -144,8 +145,8 @@ struct drm_panel {
>   	 * Backlight device, used to turn on backlight after the call
>   	 * to enable(), and to turn off backlight before the call to
>   	 * disable().
> -	 * backlight is set by drm_panel_of_backlight() and drivers
> -	 * shall not assign it.
> +	 * backlight is set by drm_panel_of_backlight() or
> +	 * drm_panel_dp_aux_backlight() and drivers shall not assign it.
>   	 */
>   	struct backlight_device *backlight;
>   
> @@ -208,11 +209,17 @@ static inline int of_drm_get_panel_orientation(const struct device_node *np,
>   #if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
>   	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
>   int drm_panel_of_backlight(struct drm_panel *panel);
> +int drm_panel_dp_aux_backlight(struct drm_panel *panel, struct drm_dp_aux *aux);
>   #else
>   static inline int drm_panel_of_backlight(struct drm_panel *panel)
>   {
>   	return 0;
>   }
> +static inline int drm_panel_dp_aux_backlight(struct drm_panel *panel,
> +					     struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
>   #endif
>   
>   #endif
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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