Re: [PATCH v2] drm/amd/display: add panel_power_savings sysfs entry to eDP connectors

[Hamza Mahfooz]

On 2/16/24 03:19, Pekka Paalanen wrote:
> On Fri, 2 Feb 2024 10:28:35 -0500
> Hamza Mahfooz <hamza.mahfooz@xxxxxxx> wrote:
>
> > We want programs besides the compositor to be able to enable or disable
> > panel power saving features.
>
> Could you also explain why, in the commit message, please?
>
> It is unexpected for arbitrary programs to be able to override the KMS
> client, and certainly new ways to do so should not be added without an
> excellent justification.
>
> Maybe debugfs would be more appropriate if the purpose is only testing
> rather than production environments?
>
> > However, since they are currently only
> > configurable through DRM properties, that isn't possible. So, to remedy
> > that issue introduce a new "panel_power_savings" sysfs attribute.
>
> When the DRM property was added, what was used as the userspace to
> prove its workings?

To my knowledge, it is only used by IGT. Also, it is worth noting that
it is a vendor specific property, so I doubt there are any compositors
out there that felt motivated enough to use it in any capacity.

> Thanks,
> pq
>
> > Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx>
> > ---
> > 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) ||
--
Hamza