linux-kernel - Re: [PATCH v3 6/9] drm/bridge: ti-sn65dsi86: Use 18-bit DP if we can

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Date:   Fri, 10 Jul 2020 12:10:58 -0500
From:   Steev Klimaszewski <steev@...i.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        David Airlie <airlied@...ux.ie>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonas Karlman <jonas@...boo.se>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Steev Klimaszewski <steev@...too.org>
Subject: Re: [PATCH v3 6/9] drm/bridge: ti-sn65dsi86: Use 18-bit DP if we can


On 7/10/20 9:47 AM, Doug Anderson wrote:
> Hi,
>
>
> But should I continue on this path,
> It's probably worth getting dithering working on your sdm845 anyway in
> case anyone actually does put a 6bpp panel on this SoC.
>
>
>> or should we be finding others who
>> have an N61 and see what their EDID reports?
> I have an email out to BOE, but it might take a little while to get a
> response.  I'll see what they say.  If they say that the panel
> actually supports 8bpp then it's a no-brainer and we should just
> switch to 8bpp and be done.
>
> ...but if they say it's a 6bpp panel that has its own dither logic
> then it gets more complicated.  Initially one would think there should
> be very little downside in defining the panel as an 8bpp panel and
> calling it done.  ...except that it conflicts with some other work
> that I have in progress.  :-P  Specifically if you treat the panel as
> 6bpp and then reduce the blanking a tiny bit you can actually save 75
> mW of total system power on my board (probably similar on your board
> since you have the same bridge chip).  You can see a patch to do that
> here:
>
> https://crrev.com/c/2276384
>
> ...so I'm hoping to get some clarity from BOE both on the true bits
> per pixel and whether my proposed timings are valid before moving
> forward.  Is that OK?
>
>
> -Doug


It's fine by me - testing Rob's suggestion of changing
MAX_HDISPLAY_SPLIT 1080->1920 along with the change to adding IS_SDM845
does give me a full screen that looks nicer, I'm fine with using the
hack locally until a proper solution is found.  And I'm always a fan of
using less power on a laptop.


I'll give the patch a spin here if you want as well.


Hopefully BOE gets back to you soon, and there's no rush, I'm just an
end user who is extremely appreciative of all the work everyone on the
list and the kernel in general put in to make my machines usable.