linux-kernel - [PATCH v3 0/3] PWM backlight interpolation adjustments

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Message-Id: <20201022050445.930403-1-amstan@chromium.org>
Date:   Wed, 21 Oct 2020 22:04:42 -0700
From:   Alexandru Stan <amstan@...omium.org>
To:     Heiko Stuebner <heiko@...ech.de>, Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Alexandru Stan <amstan@...omium.org>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org
Subject: [PATCH v3 0/3] PWM backlight interpolation adjustments

I was trying to adjust the brightness-levels for the trogdor boards:
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2291209
Like on a lot of panels, trogdor's low end needs to be cropped,
and now that we have the interpolation stuff I wanted to make use of it
and bake in even the curve that's customary to have on chromebooks.

I found the current behavior of the pwm_bl driver a little unintuitive
and non-linear. See patch 1 for a suggested fix for this.

A few veyron dts files were relying on this (perhaps weird) behavior.
Those devices also want a minimum brightness like trogdor, so changed
them to use the new way.

Finally, given that trogdor's dts is part of linux-next now, add the
brightness-levels to it, since that's the original reason I was looking at
this.

Changes in v3:
- Reordered patches, since both dts changes will work just fine
  even before the driver change.
- Rewrote a bit of the commit message to describe the new policy,
  as Daniel suggested.
- Removed redundant s64 for something that's always positive

Changes in v2:
- Fixed type promotion in the driver
- Removed "backlight: pwm_bl: Artificially add 0% during interpolation",
  userspace works just fine without it because it already knows how to use
  bl_power for turning off the display.
- Added brightness-levels to trogdor as well, now the dts is upstream.


Alexandru Stan (3):
  ARM: dts: rockchip: veyron: Remove 0 point from brightness-levels
  arm64: dts: qcom: trogdor: Add brightness-levels
  backlight: pwm_bl: Fix interpolation

 arch/arm/boot/dts/rk3288-veyron-jaq.dts      |  2 +-
 arch/arm/boot/dts/rk3288-veyron-minnie.dts   |  2 +-
 arch/arm/boot/dts/rk3288-veyron-tiger.dts    |  2 +-
 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi |  9 +++
 drivers/video/backlight/pwm_bl.c             | 70 +++++++++-----------
 5 files changed, 43 insertions(+), 42 deletions(-)

-- 
2.28.0