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

[Hamza Mahfooz <hamza.mahfooz@amd.com>]

On 2/16/24 03:19, Pekka Paalanen wrote:
> On Fri, 2 Feb 2024 10:28:35 -0500
> Hamza Mahfooz <hamza.mahfooz@amd.com> 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.

Also, to be completely honest with you, I'm not sure why it was
initially exposed as a DRM prop, since it's a power management feature.
Which is to say, that it doesn't really make sense to have the
compositor control it.

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