linux-kernel - Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

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Message-ID: <CACr-zFAVDhDvWupMMCe5ttpCU8+NSD0XK1tS=TsstM1znhDHNA@mail.gmail.com>
Date: Thu, 27 Mar 2025 13:19:16 +0000
From: Christopher Obbard <christopher.obbard@...aro.org>
To: Abel Vesa <abel.vesa@...aro.org>
Cc: Douglas Anderson <dianders@...omium.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konradybcio@...nel.org>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	Johan Hovold <johan@...nel.org>, Rui Miguel Silva <rui.silva@...aro.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

Right, the reason this was included in this series is because without
this patch the panel's backlight doesn't actually work. So for me it
was natural to include it. But happy to split it into its own series.

On Thu, 27 Mar 2025 at 08:05, Abel Vesa <abel.vesa@...aro.org> wrote:
>
> On 25-03-25 19:21:29, Christopher Obbard wrote:
> > Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> > valid non-zero MIN and MAX values. This patch reworks the logic to
> > fallback to the max value in such cases, ensuring correct backlight PWM
> > configuration even when the bit count value is not explicitly set.
> >
> > This improves compatibility with eDP panels (e.g. Samsung ATNA40YK20
> > used on the Lenovo T14s Gen6 Snapdragon with OLED panel) which reports
> > DP_EDP_PWMGEN_BIT_COUNT as 0 but still provides valid non-zero MIN/MAX
> > values.
> >
>
> Nit-pick: AFAICT, there is no relationship between this patch and the
> rest. So it should've probably not be part of this patchset.