Re: [PATCH v3 2/2] drm/tiny: add support for PIXPAPER 4.26 monochrome e-ink panel

[LiangCheng Wang <zaq14760@gmail.com>]

Hi Devarsh,

Thanks for the detailed review.

> 1) Could you please share the datasheet for the display controller used
> inside this pixpaper version ?

Unfortunately I'm not able to share the controller datasheet publicly; it
was provided to us under NDA.

> 2) Does 0xFF or 0xF7 mode work as well for your display or is it strictly
> 0xF4 which seems to mean that analog and osc bits are disabled ?

I'll test whether the standard 0xF7/0xFF sequences also work on this panel
and follow up with the result.

> 3) Also could you confirm which display controller IC does the PIXPAPER
> 4.26 use ?

The PIXPAPER 4.26 uses the Solomon SSD1677, so you're right that it is an
SSD16xx-family controller -- the commands it uses (0x01, 0x0C, 0x18, 0x20,
0x22, 0x24, 0x3C, 0x44/0x45, 0x4E/0x4F) match the standard SSD16xx set.

> it would be appropriate to add this panel as a new display panel entry in
> panel-ssd16xx.c rather than a separate driver to avoid code duplication.

I agree that consolidating SSD16xx panels under panel-ssd16xx.c is the right
long-term direction, and I'd be glad to converge there.

I'm not yet sure how SSD1677 would fit with the controllers your series
currently targets (SSD1673/SSD1680/SSD1681/SSD1683) -- ours is a larger
4.26" 800x480 panel, so I suspect it may need a new controller variant.
Would you expect panel-ssd16xx.c to be able to support SSD1677?

In the meantime, would it be reasonable to take this smaller standalone
driver, and migrate the panel into panel-ssd16xx.c once that driver lands
with SSD1677 support? I'd be happy to help with the migration, and of course
I'll defer to your and the maintainers' preference here.

Regards,
LiangCheng