Re: [PATCH v4 00/15] acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API - Uwe Kleine-König

From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Hans de Goede <hdegoede@redhat.com>
Cc: "Sam Ravnborg" <sam@ravnborg.org>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Jani Nikula" <jani.nikula@linux.intel.com>,
	"Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>,
	"Rodrigo Vivi" <rodrigo.vivi@intel.com>,
	"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	"Len Brown" <lenb@kernel.org>,
	linux-pwm@vger.kernel.org, linux-acpi@vger.kernel.org,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	dri-devel@lists.freedesktop.org,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Mika Westerberg" <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH v4 00/15] acpi/pwm/i915: Convert pwm-crc and i915 driver's PWM code to use the atomic PWM API
Date: Sat, 11 Jul 2020 08:19:01 +0200	[thread overview]
Message-ID: <20200711061901.njwx3xofo4awcflg@pengutronix.de> (raw)
In-Reply-To: <fb370663-9efe-a820-2e57-d43d3af7828c@redhat.com>

[-- Attachment #1: Type: text/plain, Size: 1827 bytes --]

Hi Hans,

On Thu, Jul 09, 2020 at 04:40:56PM +0200, Hans de Goede wrote:
> On 7/9/20 4:14 PM, Sam Ravnborg wrote:
> > On Wed, Jul 08, 2020 at 11:14:16PM +0200, Hans de Goede wrote:
> > > Here is v4 of my patch series converting the i915 driver's code for
> > > controlling the panel's backlight with an external PWM controller to
> > > use the atomic PWM API. See below for the changelog.
> > 
> > Why is it that i915 cannot use the pwm_bl driver for backlight?
> > I have not studied the code - just wondering.
> 
> The intel_panel.c code deals with 7 different types of PWM controllers
> which are built into the GPU + support for external PWM controllers
> through the kernel's PWM subsystem.
> 
> pwm_bl will work for the external PWM controller case, but not for
> the others. On top of that the intel_panel code integrates which
> the video BIOS, getting things like frequency, minimum value
> and if the range is inverted (0% duty == backlight brightness max).
> I'm not even sure if pwm_bl supports all of this, but even if it
> does the intel_panel code handles this in a unified manner for
> all supported PWM controllers, including the ones which are
> an integral part of the GPU.

pwm_bl handles inverted PWM just fine. I'm unsure what "integrates which
the video BIOS" means, but I don't see how "handling 7 different types
of PWM controllers explicitly and others using the PWM API" can be seen
as "unified manner" compared to "provide a pwm driver for whatever might
be in the GPU and then use generic code (PWM API, pwm_bl) to drive it".

Maybe I'm not understanding some involved complexity here?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]