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/ |
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