linux-kernel - Re: [PATCH v2] drm/amd/display: add panel_power

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Date: Fri, 16 Feb 2024 11:29:54 +0100
From: Christian König <ckoenig.leichtzumerken@...il.com>
To: Hamza Mahfooz <hamza.mahfooz@....com>, amd-gfx@...ts.freedesktop.org
Cc: Mario Limonciello <mario.limonciello@....com>,
 Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>,
 Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
 Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Alex Hung <alex.hung@....com>,
 Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
 Wayne Lin <wayne.lin@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/amd/display: add panel_power_savings sysfs entry
 to eDP connectors

Am 02.02.24 um 16:28 schrieb Hamza Mahfooz:
> We want programs besides the compositor to be able to enable or disable
> panel power saving features.

Well I don't know the full background, but that is usually a no-go.

> However, since they are currently only
> configurable through DRM properties, that isn't possible.

Maybe I'm repeating others, but I wanted to point it out explicitly: 
This is intentional and not that easily changeable.

If it's a common DRM property, e.g. something standardized among all 
drivers, then amdgpu is not allowed to circumvent that.

Regards,
Christian.

>   So, to remedy
> that issue introduce a new "panel_power_savings" sysfs attribute.
>
> Cc: Mario Limonciello <mario.limonciello@....com>
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
> ---
> v2: hide ABM_LEVEL_IMMEDIATE_DISABLE in the read case, force an atomic
>      commit when setting the value, call sysfs_remove_group() in
>      amdgpu_dm_connector_unregister() and add some documentation.
> ---
>   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 76 +++++++++++++++++++
>   1 file changed, 76 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 8590c9f1dda6..3c62489d03dc 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -6436,10 +6436,79 @@ int amdgpu_dm_connector_atomic_get_property(struct drm_connector *connector,
>   	return ret;
>   }
>   
> +/**
> + * DOC: panel power savings
> + *
> + * The display manager allows you to set your desired **panel power savings**
> + * level (between 0-4, with 0 representing off), e.g. using the following::
> + *
> + *   # echo 3 > /sys/class/drm/card0-eDP-1/amdgpu/panel_power_savings
> + *
> + * Modifying this value can have implications on color accuracy, so tread
> + * carefully.
> + */
> +
> +static ssize_t panel_power_savings_show(struct device *device,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct drm_connector *connector = dev_get_drvdata(device);
> +	struct drm_device *dev = connector->dev;
> +	u8 val;
> +
> +	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> +	val = to_dm_connector_state(connector->state)->abm_level ==
> +		ABM_LEVEL_IMMEDIATE_DISABLE ? 0 :
> +		to_dm_connector_state(connector->state)->abm_level;
> +	drm_modeset_unlock(&dev->mode_config.connection_mutex);
> +
> +	return sysfs_emit(buf, "%u\n", val);
> +}
> +
> +static ssize_t panel_power_savings_store(struct device *device,
> +					 struct device_attribute *attr,
> +					 const char *buf, size_t count)
> +{
> +	struct drm_connector *connector = dev_get_drvdata(device);
> +	struct drm_device *dev = connector->dev;
> +	long val;
> +	int ret;
> +
> +	ret = kstrtol(buf, 0, &val);
> +
> +	if (ret)
> +		return ret;
> +
> +	if (val < 0 || val > 4)
> +		return -EINVAL;
> +
> +	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> +	to_dm_connector_state(connector->state)->abm_level = val ?:
> +		ABM_LEVEL_IMMEDIATE_DISABLE;
> +	drm_modeset_unlock(&dev->mode_config.connection_mutex);
> +
> +	drm_kms_helper_hotplug_event(dev);
> +
> +	return count;
> +}
> +
> +static DEVICE_ATTR_RW(panel_power_savings);
> +
> +static struct attribute *amdgpu_attrs[] = {
> +	&dev_attr_panel_power_savings.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group amdgpu_group = {
> +	.name = "amdgpu",
> +	.attrs = amdgpu_attrs
> +};
> +
>   static void amdgpu_dm_connector_unregister(struct drm_connector *connector)
>   {
>   	struct amdgpu_dm_connector *amdgpu_dm_connector = to_amdgpu_dm_connector(connector);
>   
> +	sysfs_remove_group(&connector->kdev->kobj, &amdgpu_group);
>   	drm_dp_aux_unregister(&amdgpu_dm_connector->dm_dp_aux.aux);
>   }
>   
> @@ -6541,6 +6610,13 @@ amdgpu_dm_connector_late_register(struct drm_connector *connector)
>   		to_amdgpu_dm_connector(connector);
>   	int r;
>   
> +	if (connector->connector_type == DRM_MODE_CONNECTOR_eDP) {
> +		r = sysfs_create_group(&connector->kdev->kobj,
> +				       &amdgpu_group);
> +		if (r)
> +			return r;
> +	}
> +
>   	amdgpu_dm_register_backlight_device(amdgpu_dm_connector);
>   
>   	if ((connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort) ||