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

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Date: Sat, 27 Jan 2024 23:38:28 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Hamza Mahfooz <hamza.mahfooz@....com>, amd-gfx@...ts.freedesktop.org
Cc: 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] drm/amd/display: add panel_power_savings sysfs entry to
 eDP connectors

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@....com>
>> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
>> ---
>>   .../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) ||
>