From: Hans de Goede <hdegoede@redhat.com>
To: Simon Ser <contact@emersion.fr>
Cc: Sebastian Wick <sebastian.wick@redhat.com>,
Martin Roukala <martin.roukala@mupuf.org>,
Christoph Grenz <christophg+lkml@grenz-bonn.de>,
wayland <wayland-devel@lists.freedesktop.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Yusuf Khan <yusisamerican@gmail.com>
Subject: Re: [RFC] drm/kms: control display brightness through drm_connector properties
Date: Mon, 11 Apr 2022 12:35:20 +0200 [thread overview]
Message-ID: <2e4963f6-6746-082d-c516-6fb73307cd18@redhat.com> (raw)
In-Reply-To: <XwpYE-RK1zRFJfojeMJV5ddsxHnHg4HRTXd4fZ_7yUMBZRCy3ARRIPC6Y-eCJ5Ag9Fin8FGLz6t-L8Ix4P7ykQlrJ6dH4LYye20kyHKtVaI=@emersion.fr>
Hi Simon,
On 4/8/22 10:22, Simon Ser wrote:
> Hi Hans,
>
> Thanks for your details replies!
>
> On Thursday, April 7th, 2022 at 19:43, Hans de Goede <hdegoede@redhat.com> wrote:
>
>>> On Thursday, April 7th, 2022 at 17:38, Hans de Goede <hdegoede@redhat.com> wrote:
>>>
>>>> The drm_connector brightness properties
>>>> =======================================
>>>>
>>>> bl_brightness: rw 0-int32_max property controlling the brightness setting
>>>> of the connected display. The actual maximum of this will be less then
>>>> int32_max and is given in bl_brightness_max.
>>>
>>> Do we need to split this up into two props for sw/hw state? The privacy screen
>>> stuff needed this, but you're pretty familiar with that. :)
>>
>> Luckily that won't be necessary, since the privacy-screen is a security
>> feature the firmware/embedded-controller may refuse our requests
>> (may temporarily lock-out changes) and/or may make changes without
>> us requesting them itself. Neither is really the case with the
>> brightness setting of displays.
>
> Cool, makes sense to me!
>
>>>> bl_brightness_max: ro 0-int32_max property giving the actual maximum
>>>> of the display's brightness setting. This will report 0 when brightness
>>>> control is not available (yet).
>>>
>>> I don't think we actually need that one. Integer KMS props all have a
>>> range which can be fetched via drmModeGetProperty. The max can be
>>> exposed via this range. Example with the existing alpha prop:
>>>
>>> "alpha": range [0, UINT16_MAX] = 65535
>>
>> Right, I already knew that, which is why I explicitly added a range
>> to the props already. The problem is that the range must be set
>> before registering the connector and when the backlight driver
>> only shows up (much) later during boot then we don't know the
>> range when registering the connector. I guess we could "patch-up"
>> the range later. But AFAIK that would be a bit of abuse of the
>> property API as the range is intended to never change, not
>> even after hotplug uevents. At least atm there is no infra
>> in the kernel to change the range later.
>>
>> Which is why I added an explicit bl_brightness_max property
>> of which the value gives the actual effective maximum of the
>> brightness.
>>
>> I did consider using the range for this and updating it
>> on the fly I think nothing is really preventing us from
>> doing so, but it very much feels like abusing the generic
>> properties API.
>
> Since this is new uAPI there's no concern about backwards compat here. So it's
> pretty much a matter of how we want the uAPI to look like. I was suggesting
> using a range because it's self-describing, but maybe it's an abuse.
>
> Daniel Vetter, what do you think? If a property's range is going to be updated
> on the fly, should we go for it, or should we use a separate prop to describe
> the max value?
Daniel, as explained in my replies to you, I do believe that dynamically
updating the range is unavoidable. Especially once we also add support
for setting a monitor's brightness over DDC/CI.
Since external monitors (with/without DDC/CI support) can come and go and
since properties cannot be added/removed after connector registration, we
need a way to let userspace know if brightness control is actually available
or not and what the range is. We can use a max value of 0 for not available
and other values for the actual range, which I believe is a sane API.
But the question from Simon then still remains, do we update the range
of the property on the fly, followed by a connector hotplug uevent; or
do we use a separate brightness_max property for this?
Note that as Rasterman indicated that with DDC/CI support we could also
offer other properties (for which I see no reason atm) and if we do
say also add a contrast property over DDC/CI then if we go the
separate brightness_max route that would mean adding 2 props for
each setting which we want to support.
Regards,
Hans
next prev parent reply other threads:[~2022-04-11 10:35 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 15:38 [RFC] drm/kms: control display brightness through drm_connector properties Hans de Goede
2022-04-07 16:51 ` Simon Ser
2022-04-07 17:43 ` Hans de Goede
2022-04-07 21:05 ` Alex Deucher
2022-04-08 8:07 ` Daniel Vetter
2022-04-08 9:58 ` Hans de Goede
2022-04-08 10:09 ` Hans de Goede
2022-04-08 10:16 ` Simon Ser
2022-04-08 10:26 ` Hans de Goede
2022-04-13 8:32 ` Daniel Vetter
2022-04-13 8:38 ` Simon Ser
2022-04-13 9:44 ` Hans de Goede
2022-04-08 10:23 ` Hans de Goede
2022-04-08 14:08 ` Alex Deucher
2022-04-08 14:55 ` Hans de Goede
2022-04-08 15:11 ` Alex Deucher
2022-04-11 10:18 ` Hans de Goede
2022-04-11 11:34 ` Pekka Paalanen
2022-04-11 11:50 ` Hans de Goede
2022-04-11 13:11 ` Mikhail Gusarov
2022-04-11 14:11 ` Alex Deucher
2022-04-14 10:24 ` Jani Nikula
2022-04-27 14:03 ` Daniel Vetter
2022-04-27 14:23 ` Jani Nikula
2022-04-27 14:26 ` Daniel Vetter
2022-04-29 8:55 ` Hans de Goede
2022-04-29 8:59 ` Simon Ser
2022-04-29 9:06 ` Pekka Paalanen
2022-04-29 9:49 ` Lattannavar, Sameer
2022-04-08 8:22 ` Simon Ser
2022-04-08 15:00 ` Hans de Goede
2022-04-11 10:35 ` Hans de Goede [this message]
2022-04-07 18:58 ` Carsten Haitzler
2022-04-11 10:27 ` Hans de Goede
2022-04-11 11:14 ` Carsten Haitzler
2022-04-14 13:10 ` Jani Nikula
2022-05-18 12:59 ` Hans de Goede
2022-05-18 14:23 ` Jani Nikula
2022-05-31 10:40 ` Hans de Goede
2022-05-18 14:40 ` Ville Syrjälä
2022-08-24 2:18 ` Yusuf Khan
2022-08-25 8:27 ` Hans de Goede
2022-08-25 21:40 ` Yusuf Khan
2022-08-28 8:08 ` Hans de Goede
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