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

[Mario Limonciello]

On 1/26/2024 16:34, Mario Limonciello wrote:
> On 1/26/2024 16:22, Hamza Mahfooz wrote:
> > We want programs besides the compositor to be able to enable or disable
> > panel power saving features. 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.
> >
> > Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@xxxxxxx>
> > ---
> >   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 59 +++++++++++++++++++
> >   1 file changed, 59 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 cd98b3565178..b3fcd833015d 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -6534,6 +6534,58 @@ 
> > amdgpu_dm_connector_atomic_duplicate_state(struct drm_connector 
> > *connector)
> >       return &new_state->base;
> >   }
> > +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;
> > +    ssize_t val;
> > +
> > +    drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> > +    val = to_dm_connector_state(connector->state)->abm_level;
> > +    drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > +
> > +    return sysfs_emit(buf, "%lu\n", val);

When the system is first booted up with nothing on the kernel command 
line, this emits the value for ABM_LEVEL_IMMEDIATE_DISABLE, which isn't 
something we normally should be showing to people.

I think you should be special casing it similar to how the store special 
case works.

> > +}
> > +
> > +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);
> > +

It appears that the ABM doesn't actually take effect by writing this 
value until the next modeset.
This is also reported by Dominik Förderer.  I suggested he try to change 
resolutions in his DE and that activated ABM.

So I think it's missing another call to flush out to the hardware.

> > +    return count;
> > +}
> > +
>
> To make this more discoverable I think you want some kerneldoc.
>
> > +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 int
> >   amdgpu_dm_connector_late_register(struct drm_connector *connector)
> >   {
> > @@ -6541,6 +6593,13 @@ 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;
> > +    }
> > +
>
> I think there should be some matching code sysfs_remove_group(), maybe 
> in early_unregister() callback.
>
> >       amdgpu_dm_register_backlight_device(amdgpu_dm_connector);
> >       if ((connector->connector_type == 
> > DRM_MODE_CONNECTOR_DisplayPort) ||