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

Sam Ravnborg
2020-07-09T15:23:21Z

Hi,
On Thu, Jul 09, 2020 at 04:40:56PM +0200, Hans de Goede wrote:
> Hi,
>
> On 7/9/20 4:14 PM, Sam Ravnborg wrote:
> > Hi Hans.
> >
> > On Wed, Jul 08, 2020 at 11:14:16PM +0200, Hans de Goede wrote:
> > > Hi All,
> > >
> > > 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.

Thanks for the explanation.
This is a more complicated world than the usual embedded case with a
single pwm, no BIOS etc. So it makes sense.

Sam

>
> Regards,
>
> Hans
>
>
>
> > > Initially the plan was for this series to consist of 2 parts:
> > > 1. convert the pwm-crc driver to support the atomic PWM API and
> > > 2. convert the i915 driver's PWM code to use the atomic PWM API.
> > >
> > > But during testing I've found a number of bugs in the pwm-lpss and I
> > > found that the acpi_lpss code needs some special handling because of
> > > some ugliness found in most Cherry Trail DSDTs.
> > >
> > > So now this series has grown somewhat large and consists of 4 parts:
> > >
> > > 1. acpi_lpss fixes workarounds for Cherry Trail DSTD nastiness
> > > 2. various fixes to the pwm-lpss driver
> > > 3. convert the pwm-crc driver to support the atomic PWM API and
> > > 4. convert the i915 driver's PWM code to use the atomic PWM API
> > >
> > > The involved acpi_lpss and pwm drivers do not see a whole lot of churn,
> > > so the plan is to merge this all through drm-intel-next-queued (dinq)
> > > once all the patches are reviewed / have acks.
> > >
> > > In v4 the ACPI patches have been Acked by Rafael and the i915 patches
> > > have been acked by Jani. So that just leaves the PWM patches.
> > >
> > > Uwe can I get your ok / ack for merging this through the dinq branch
> > > once you have acked al the PWM patches ?
> > >
> > > This series has been tested (and re-tested after adding various bug-fixes)
> > > extensively. It has been tested on the following devices:
> > >
> > > -Asus T100TA BYT + CRC-PMIC PWM
> > > -Toshiba WT8-A BYT + CRC-PMIC PWM
> > > -Thundersoft TS178 BYT + CRC-PMIC PWM, inverse PWM
> > > -Asus T100HA CHT + CRC-PMIC PWM
> > > -Terra Pad 1061 BYT + LPSS PWM
> > > -Trekstor Twin 10.1 BYT + LPSS PWM
> > > -Asus T101HA CHT + CRC-PMIC PWM
> > > -GPD Pocket CHT + CRC-PMIC PWM
> > >
> > > Changelog:
> > >
> > > Changes in v2:
> > > - Fix coverletter subject
> > > - Drop accidentally included debugging patch
> > > - "[PATCH v3 02/15] ACPI / LPSS: Save Cherry Trail PWM ctx registers only once (
> > > - Move #define LPSS_SAVE_CTX_ONCE define to group it with LPSS_SAVE_CTX
> > >
> > > Changes in v3:
> > > - "[PATCH v3 04/15] pwm: lpss: Add range limit check for the base_unit register value"
> > > - Use base_unit_range - 1 as maximum value for the clamp()
> > > - "[PATCH v3 05/15] pwm: lpss: Use pwm_lpss_apply() when restoring state on resume"
> > > - This replaces the "pwm: lpss: Set SW_UPDATE bit when enabling the PWM"
> > > patch from previous versions of this patch-set, which really was a hack
> > > working around the resume issue which this patch fixes properly.
> > > - PATCH v3 6 - 11 pwm-crc changes:
> > > - Various small changes resulting from the reviews by Andy and Uwe,
> > > including some refactoring of the patches to reduce the amount of churn
> > > in the patch-set
> > >
> > > Changes in v4:
> > > - "[PATCH v4 06/16] pwm: lpss: Correct get_state result for base_unit == 0"
> > > - This is a new patch in v4 of this patchset
> > > - "[PATCH v4 12/16] pwm: crc: Implement get_state() method"
> > > - Use DIV_ROUND_UP when calculating the period and duty_cycle values
> > > - "[PATCH v4 16/16] drm/i915: panel: Use atomic PWM API for devs with an external PWM controller"
> > > - Add a note to the commit message about the changes in pwm_disable_backlight()
> > > - Use the pwm_set/get_relative_duty_cycle() helpers
> > >
> > > Regards,
> > >
> > > Hans
> > >
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> >