linux-kernel - Re: [PATCH 0/2] Add backlight-pwm-passthru in analogix DP driver

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Date:   Fri, 16 Mar 2018 12:50:21 -0400
From:   Sean Paul <seanpaul@...omium.org>
To:     Alexandru M Stan <amstan@...omium.org>
Cc:     David Airlie <airlied@...ux.ie>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Sean Paul <seanpaul@...omium.org>, devicetree@...r.kernel.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Heiko Stuebner <heiko@...ech.de>, briannorris@...omium.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        dianders@...omium.org, linux-rockchip@...ts.infradead.org,
        marcheu@...omium.org, hoegsberg@...omium.org,
        Thierry Escande <thierry.escande@...labora.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        Yakir Yang <kuankuan.y@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        zain wang <wzz@...k-chips.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 0/2] Add backlight-pwm-passthru in analogix DP driver

On Thu, Mar 15, 2018 at 07:56:57PM -0700, Alexandru M Stan wrote:
> I noticed that the backlight on the ASUS Chromebook Flip C101 (bob) is
> flickering.
> 
> We're sending it a high frequency pwm signal, but the EDP panel decided to
> "parse" the signal, read the duty cycle, then make its own signal that
> it sends to the LEDs.
> 
> So even though we send a nice high refresh rate at 1200Hz, the panel backlight
> flickers at 200Hz (which is not even divisible by the 60Hz refresh rate).
> 
> The fix for that is to enable the EDP_BACKLIGHT_FREQ_PWM_PIN_PASSTHRU bit from
> the DPCD EDP registers. This makes the panel actually follow the signal
> we're giving it.
> 
> This series includes the optional dt binding to enable this fix
> (backlight-pwm-passthru) and the corresponding code in the analogix
> drm/bridge driver.
> 

Thanks for sending these patches!

With Archit and Daniel's comments addressed, feel free to add my 

Reviewed-by: Sean Paul <seanpaul@...omium.org>

> 
> Alexandru M Stan (2):
>   dt-bindings: analogix-dp: Add backlight-pwm-passthru
>   drm/bridge: analogix: Enable EDP_BACKLIGHT_FREQ_PWM_PIN_PASSTHRU
> 
>  .../bindings/display/bridge/analogix_dp.txt        |  4 ++
>  drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 48 ++++++++++++++++++++++
>  drivers/gpu/drm/bridge/analogix/analogix_dp_core.h |  1 +
>  3 files changed, 53 insertions(+)
> 
> -- 
> 2.13.5
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS