linux-kernel - Re: [PATCH v3 0/2] drm: minimum backlight overrides and implementation for amdgpu

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Message-ID: <Zqqku_zS7CpPGbzW@phenom.ffwll.local>
Date: Wed, 31 Jul 2024 22:55:23 +0200
From: Daniel Vetter <daniel.vetter@...ll.ch>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Harry Wentland <harry.wentland@....com>,
	Leo Li <sunpeng.li@....com>,
	Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
	Mario Limonciello <mario.limonciello@....com>,
	Matt Hartley <matt.hartley@...il.com>,
	Kieran Levin <ktl@...mework.net>,
	Hans de Goede <hdegoede@...hat.com>,
	Xinhui Pan <Xinhui.Pan@....com>, amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Dustin Howett <dustin@...ett.net>
Subject: Re: [PATCH v3 0/2] drm: minimum backlight overrides and
 implementation for amdgpu

On Wed, Jul 31, 2024 at 08:40:12PM +0300, Jani Nikula wrote:
> On Wed, 31 Jul 2024, Thomas Weißschuh <linux@...ssschuh.net> wrote:
> > The value of "min_input_signal" returned from ATIF on a Framework AMD 13
> > is "12". This leads to a fairly bright minimum display backlight.
> >
> > Add a generic override helper for the user to override the settings
> > provided by the firmware through the kernel cmdline.
> > Also add amdgpu as a user of that helper.
> >
> > One solution would be a fixed firmware version, which was announced but
> > has no timeline.
> 
> The flip side is that if we add this now, it pretty much has a timeline:
> We'll have to carry and support it forever.
> 
> It's not a great prospect for something so specific. Not to mention that
> the limits are generally there for electrical minimums that should not
> be overridden. And before you know it, we'll have bug reports about
> flickering screens...

Yeah I think for this specific case where a fixed firmware is already
kinda promised, a quirk is the right fix. Otherwise we open up a can of
worms here ... so personally I like v2 a lot more.
-Sima

> 
> BR,
> Jani.
> 
> 
> >
> > This helper does conflict with the mode override via the cmdline.
> > Only one can be specified.
> > IMO the mode override can be extended to also handle "min-brightness"
> > when that becomes necessary.
> >
> > ---
> > Changes in v3:
> > - Switch to cmdline override parameter
> > - Link to v2: https://lore.kernel.org/r/20240623-amdgpu-min-backlight-quirk-v2-0-cecf7f49da9b@weissschuh.net
> >
> > Changes in v2:
> > - Introduce proper drm backlight quirk infrastructure
> > - Quirk by EDID and DMI instead of only DMI
> > - Limit quirk to only single Framework 13 matte panel
> > - Link to v1: https://lore.kernel.org/r/20240610-amdgpu-min-backlight-quirk-v1-1-8459895a5b2a@weissschuh.net
> >
> > ---
> > Thomas Weißschuh (2):
> >       drm/connector: add drm_connector_get_cmdline_min_brightness_override()
> >       drm/amd/display: implement minimum brightness override
> >
> >  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  6 ++++
> >  drivers/gpu/drm/drm_connector.c                   | 34 +++++++++++++++++++++++
> >  include/drm/drm_connector.h                       |  2 ++
> >  3 files changed, 42 insertions(+)
> > ---
> > base-commit: 36821612eb3091a21f7f4a907b497064725080c3
> > change-id: 20240610-amdgpu-min-backlight-quirk-8402fd8e736a
> >
> > Best regards,
> 
> -- 
> Jani Nikula, Intel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch