RE: [PATCH v2 0/2] Add waveshare 7inch touchscreen panel support

[Shengyang Chen]

Hi, Dave

Thanks for your comment

> -----Original Message-----
> From: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> Sent: 2024年1月10日 1:29
> To: neil.armstrong@xxxxxxxxxx
> Cc: Shengyang Chen <shengyang.chen@xxxxxxxxxxxxxxxx>;
> devicetree@xxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx;
> quic_jesszhan@xxxxxxxxxxx; sam@xxxxxxxxxxxx; airlied@xxxxxxxxx;
> daniel@xxxxxxxx; maarten.lankhorst@xxxxxxxxxxxxxxx; mripard@xxxxxxxxxx;
> tzimmermann@xxxxxxx; robh+dt@xxxxxxxxxx;
> krzysztof.kozlowski+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx; wahrenst@xxxxxxx;
> thierry.reding@xxxxxxxxx; Changhuang Liang
> <changhuang.liang@xxxxxxxxxxxxxxxx>; Keith Zhao
> <keith.zhao@xxxxxxxxxxxxxxxx>; Jack Zhu <jack.zhu@xxxxxxxxxxxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 0/2] Add waveshare 7inch touchscreen panel support
> 
> Hi
> 
> On Tue, 9 Jan 2024 at 11:19, <neil.armstrong@xxxxxxxxxx> 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?
> 

Actually, the mode fixup method is referred and used in DSI's new patch
https://patchwork.kernel.org/project/dri-devel/patch/20240109072516.24328-3-shengyang.chen@xxxxxxxxxxxxxxxx/
you can check it in cdns_dsi_jh7110_update()
This code is being reviewed and may need to be optimized later.

And the timing in this panel patch is tested and verified but we did not try other timing. Sorry about that.
As Stefan suggested, we should try other timing from panel-simple for example "powertip,ph800480t013-idf02".

If the other timing from panel-simple can be used, maybe it is not necessary for us to submit panel timing patch.

>   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@xxxxxxxxxxxxxxxx/
> > >
> > > 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(+)
> > >
> >

Best Regards,
Shengyang