linux-kernel - Re: [Freedreno] [RFC PATCH 00/13] drm/msm: Add Display Stream Compression Support

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Date:   Thu, 03 Jun 2021 16:40:35 -0700
From:   abhinavk@...eaurora.org
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Rob Clark <robdclark@...il.com>, DTML <devicetree@...r.kernel.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        David Airlie <airlied@...ux.ie>,
        MSM <linux-arm-msm@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:DRM PANEL DRIVERS" <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        freedreno <freedreno@...ts.freedesktop.org>
Subject: Re: [Freedreno] [RFC PATCH 00/13] drm/msm: Add Display Stream
 Compression Support

On 2021-06-02 04:01, Vinod Koul wrote:
> On 27-05-21, 16:30, Rob Clark wrote:
>> On Wed, May 26, 2021 at 8:00 AM Jeffrey Hugo 
>> <jeffrey.l.hugo@...il.com> wrote:
>> > On Tue, May 25, 2021 at 11:46 PM Vinod Koul <vkoul@...nel.org> wrote:
> 
>> > Frankly, I don't like the MSM ACPI solution that I've seen on the laptops.
>> > The ACPI assumes the entire MDSS (including DSI parts) and GPU is one
>> > device, and ultimately handled by one driver.  That driver needs to
>> > get a value from UEFI (set by the bootloader) that is the "panel id".
>> > Then the driver calls into ACPI (I think its _ROM, but I might be
>> > mistaken, doing this from memory) with that id.  It gets back a binary
>> > blob which is mostly an xml file (format is publicly documented) that
>> > contains the panel timings and such.
>> 
>> tbh, I kinda suspect that having a single "gpu" device (which also
>> includes venus, in addition to display, IIRC) in the ACPI tables is a
>> windowsism, trying to make things look to userspace like a single "GPU
>> card" in the x86 world.. but either way, I think the ACPI tables on
>> the windows arm laptops which use dsi->bridge->edp is too much of a
>> lost cause to even consider here.  Possibly ACPI boot on these devices
>> would be more feasible on newer devices which have direct eDP out of
>> the SoC without requiring external bridge/panel glue.
> 
> yeah that is always a very different world. although it might make 
> sense
> to use information in tables and try to deduce information about the
> system can be helpful...
> 
>> I'd worry more about what makes sense in a DT world, when it comes to
>> DT bindings.
> 
> And do you have thoughts on that..?

At the moment, I will comment on the bindings first and my idea on how 
to proceed.
The bindings mentioned here: 
https://lore.kernel.org/dri-devel/20210521124946.3617862-3-vkoul@kernel.org/ 
seem to be just
taken directly from downstream which was not the plan.

I think all of these should be part of the generic panel bindings as 
none of these are QC specific:

@@ -188,6 +195,14 @@ Example:
  		qcom,master-dsi;
  		qcom,sync-dual-dsi;

+		qcom,mdss-dsc-enabled;
+		qcom,mdss-slice-height = <16>;
+		qcom,mdss-slice-width = <540>;
+		qcom,mdss-slice-per-pkt = <1>;
+		qcom,mdss-bit-per-component = <8>;
+		qcom,mdss-bit-per-pixel = <8>;
+		qcom,mdss-block-prediction-enable;
+

How about having a panel-dsc.yaml which will have these properties and 
have a panel-dsc node to have this information?

I would like to hear the feedback on this proposal then the series can 
be reworked.

Thanks

Abhinav