linux-kernel - Re: [PATCH v2 0/2] Add waveshare 7inch touchscreen panel support

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Date: Tue, 9 Jan 2024 17:28:44 +0000
From: Dave Stevenson <dave.stevenson@...pberrypi.com>
To: neil.armstrong@...aro.org
Cc: Shengyang Chen <shengyang.chen@...rfivetech.com>, devicetree@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, quic_jesszhan@...cinc.com, sam@...nborg.org, 
	airlied@...il.com, daniel@...ll.ch, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, robh+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, wahrenst@....net, 
	thierry.reding@...il.com, changhuang.liang@...rfivetech.com, 
	keith.zhao@...rfivetech.com, jack.zhu@...rfivetech.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Add waveshare 7inch touchscreen panel support

Hi

On Tue, 9 Jan 2024 at 11:19, <neil.armstrong@...aro.org> wrote:
>
> Hi,
>
> On 09/01/2024 08:09, Shengyang Chen wrote:
> > This patchset adds waveshare 7inch touchscreen panel support
> > for the StarFive JH7110 SoC.
>
> Could you precise which SKU you're referring to ? is it 19885 => https://www.waveshare.com/7inch-dsi-lcd.htm ?
>
> Are you sure it requires different timings from the RPi one ? In the Waveshare
> wiki it explicitly uses the rpi setup (vc4-kms-dsi-7inch) to drive it: https://www.waveshare.com/wiki/7inch_DSI_LCD

I raise the same question.

Keith Zhao earlier submitted effectively the same set of patches [1]
and the response for the updated timing was:
<quote>
My platform dphy tx hardware has certain limitations.
Only supports integer multiples of 10M bitrate:
such as 160M ,170M, 180M,190M,...1G(max)

as common dphy bitrate = pixclock*bpp/lanes.
This value cannot match successfully in most cases.

so in order to match bitrate , I choose a bitrate value around
pixclock*bpp/lanes,
Prevent overflow and underflow by fine-tuning the timing parameters:-(
that will make the new timming value.
</quote>

I then suggested mode_fixup should be used in the DSI host driver, and
Keith acknowledged that.

Is this new timing still because of the DSI host requirement?

  Dave

[1] https://lists.freedesktop.org/archives/dri-devel/2023-December/434150.html

> Neil
>
> >
> >
> > changes since v1:
> > - Rebased on tag v6.7.
> >
> > patch 1:
> > - Gave up original changing.
> > - Changed the commit message.
> > - Add compatible in panel-simple.yaml
> >
> > patch 2:
> > - Gave up original changing.
> > - Changed the commit message.
> > - Add new mode for the panel in panel-simple.c
> >
> > v1: https://patchwork.kernel.org/project/dri-devel/cover/20231124104451.44271-1-shengyang.chen@starfivetech.com/
> >
> > Shengyang Chen (2):
> >    dt-bindings: display: panel: panel-simple: Add compatible property for
> >      waveshare 7inch touchscreen panel
> >    gpu: drm: panel: panel-simple: add new display mode for waveshare
> >      7inch touchscreen panel
> >
> >   .../bindings/display/panel/panel-simple.yaml  |  2 ++
> >   drivers/gpu/drm/panel/panel-simple.c          | 28 +++++++++++++++++++
> >   2 files changed, 30 insertions(+)
> >
>