linux-kernel - Re: [PATCH 0/3] drm/i915 / LPSS / mfd: Select correct PWM controller to use based on VBT

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Date:   Tue, 19 Nov 2019 18:32:16 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Lee Jones <lee.jones@...aro.org>,
        linux-acpi@...r.kernel.org,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] drm/i915 / LPSS / mfd: Select correct PWM controller
 to use based on VBT

On Tue, Nov 19, 2019 at 04:18:15PM +0100, Hans de Goede wrote:
> Hi All,
> 
> This series needs to be merged through a single tree, to keep things
> bisectable. I have even considered just squashing all 3 patches into 1,
> but having separate commits seems better, but that does lead to an
> intermediate state where the backlight sysfs interface will be broken
> (and fixed 2 commits later). See below for some background info.
> 
> The changes to drivers/acpi/acpi_lpss.c and drivers/mfd/intel_soc_pmic_core.c
> are quite small and should not lead to any conflicts, so I believe that
> it would be best to merge this entire series through the drm-intel tree.
> 
> Lee, may I have your Acked-by for merging the mfd change through the
> drm-intel tree?
> 
> Rafael, may I have your Acked-by for merging the acpi_lpss change through the
> drm-intel tree?
> 

Entire series (or a single patch) makes sense to me.
Thanks for fixing this old hardware!

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> Regards,
> 
> Hans
> 
> p.s.
> 
> The promised background info:
> 
> We have this long standing issue where instead of looking in the i915
> VBT (Video BIOS Table) to see if we should use the PWM block of the SoC
> or of the PMIC to control the backlight of a DSI panel, we rely on
> drivers/acpi/acpi_lpss.c and/or drivers/mfd/intel_soc_pmic_core.c
> registering a pwm with the generic name of "pwm_backlight" and then the
> i915 panel code does a pwm_get(dev, "pwm_backlight").
> 
> We have some heuristics in drivers/acpi/acpi_lpss.c to not register the
> lookup if a Crystal Cove PMIC is presend and the mfd/intel_soc_pmic_core.c
> code simply assumes that since there is a PMIC the PMIC PWM block will
> be used. Basically we are winging it.
> 
> Recently I've learned about 2 different BYT devices:
> Point of View MOBII TAB-P800W
> Acer Switch 10 SW5-012
> 
> Which use a Crystal Cove PMIC, yet the LCD is connected to the SoC/LPSS
> PWM controller (and the VBT correctly indicates this), so here our old
> heuristics fail.
> 
> This series renams the PWM lookups registered by the LPSS /
> intel_soc_pmic_core.c code from "pwm_backlight" to "pwm_soc_backlight" resp.
> "pwm_pmic_backlight" and in the LPSS case also dropping the heuristics when
> to register the lookup. This combined with teaching the i915 panel to call
> pwm_get for the right lookup-name depending on the VBT bits resolves this.
> 

-- 
With Best Regards,
Andy Shevchenko