Re: [PATCH v5] drm/panel: db7430: Add driver for Samsung DB7430

[Linus Walleij <linus.walleij@linaro.org>]

On Fri, Jun 11, 2021 at 12:30 AM Doug Anderson <dianders@chromium.org> wrote:

> > +       mipi_dbi_command(dbi, MIPI_DCS_SET_ADDRESS_MODE, 0x0a);
>
> I would still prefer it if there was some type of error checking since
> SPI commands can fail and could potentially fail silently. What about
> at least this (untested):
>
> #define db7430_dbi_cmd(_db, _cmd, _seq...) \
>   do {
>     int _ret = mipi_dbi_command(_db->dbi, _cmd, _seq);
>     if (_ret)
>       dev_warn(_db->dev, "DBI cmd %d failed (%d)\n", _cmd, _ret);
>   } while (0)
>
> Then at least you know _something_ will show up in the logs if there's
> a transfer failure instead of silence?
>
> If you truly don't want the error checking then I guess I won't
> insist, but it feels like the kind of thing that will bite someone
> eventually... In any case, I'm happy to add this now (especially since
> the DBI stuff is Acked now).

This looks more like something that should be done in
mipi_dbi_command() in include/drm/drm_mipi_dbi.h
which claims:

 * Returns:
 * Zero on success, negative error code on failure.
 */

But no it does not return anything:

#define mipi_dbi_command(dbi, cmd, seq...) \
({ \
        const u8 d[] = { seq }; \
        mipi_dbi_command_stackbuf(dbi, cmd, d, ARRAY_SIZE(d)); \
})

I'll fix up the include and apply then we can think about
what to do with mipi_dbi_command().

Yours,
Linus Walleij