[PATCH 3/3] drm/mipi: use dcs write for mipi_dsi_dcs_set_tear_scanline

[Emil Velikov]

Hi Vinay,

On Thu, 7 May 2020 at 17:18, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>
> On Thu, 7 May 2020 at 13:29, Vinay Simha B N <simhavcs at gmail.com> wrote:
> >
> > Emil,
> >
> > Reply inline
> >
> > On Tue, 5 May 2020 at 9:35 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> >>
> >> From: Emil Velikov <emil.velikov at collabora.com>
> >>
> >> The helper uses the MIPI_DCS_SET_TEAR_SCANLINE, although it's currently
> >> using the generic write. This does not look right.
> >>
> >> Perhaps some platforms don't distinguish between the two writers?
> >>
> >> Cc: Robert Chiras <robert.chiras at nxp.com>
> >> Cc: Vinay Simha BN <simhavcs at gmail.com>
> >> Cc: Jani Nikula <jani.nikula at intel.com>
> >> Cc: Thierry Reding <treding at nvidia.com>
> >> Fixes: e83950816367 ("drm/dsi: Implement set tear scanline")
> >> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
> >> ---
> >> Robert, can you please test this against the only user - the Raydium
> >> RM67191 panel driver that you introduced.
> >>
> >> Thanks
> >>
> >> Vinay, can you confirm if this is a genuine typo or there's something
> >> really subtle happening.
> >
> > this has been tested on nexus 7 with jdi panel.
> The jdi panel (JDI LT070ME05000 I believe) does not use the function, hmm.
>
> Looking through the ML archive - the call in the first 4 revisions of the patch.
> Then with v5 it has magically disappeared alongside mipi_dsi_dcs_set_tear_on().
>
> No comment explaining why though - does the driver work w/o both of those?
>
Any ideas, does the driver work in today's state?

> > I did not understand what is the typo here?
> > We need to use DC’s write instead of generic write?
>
> I believe the clue is in the command name - MIPI_DSI_DCS. I was going
> to double-check with the spec although it's members only :-\
> Based on the usage in DRM, all DCS commands are issued via
> mipi_dsi_dcs_{read,write}
>
Do you agree with the rationale? Alternatively, do you have a
reference to the Android tree where the generic write is used.

Thanks
Emil