linux-kernel - Re: [PATCH] drm/msm/dp: add module parameter for PSR

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Message-ID: <ZG4dry_GOJPSyrWC@hovoldconsulting.com>
Date:   Wed, 24 May 2023 16:22:39 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Douglas Anderson <dianders@...omium.org>,
        freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, quic_jesszhan@...cinc.com,
        swboyd@...omium.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: add module parameter for PSR

On Wed, May 24, 2023 at 11:06:03AM +0300, Dmitry Baryshkov wrote:
> On 24/05/2023 09:59, Johan Hovold wrote:

> > Regressions happen and sometimes there are corner cases that are harder
> > to find, but this is a breakage of a fundamental feature that was
> > reported before the code was even merged into mainline.
> > 
> >> We should have ideally gone with the modparam with the feature patches
> >> itself knowing that it gets enabled for all sinks if PSR is supported.
> > 
> > Modparams are things of the past should not be used to enable broken
> > features so that some vendor can tick of their internal lists of
> > features that have been "mainlined".
> 
> We have had a history of using modparam with i915 and IIRC amdgpu / 
> radeon drivers to allow users to easily check whether new feature works 
> for their hardware. My current understanding is that PSR+VT works for on 
> some laptops and doesn't on some other laptops, which makes it a valid case.

But here it does not seem to be the hardware that's the issue, but
rather that the implementation is incorrect or incomplete.

Johan