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SubjectRe: [PATCH 3/3] drm/panel: add panel driver for Xinpeng XPP055C272 panels
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Hi Sam,

Am Sonntag, 15. Dezember 2019, 09:29:16 CET schrieb Sam Ravnborg:
> Hi Heiko.
>
> > Am Samstag, 14. Dezember 2019, 09:17:30 CET schrieb Sam Ravnborg:
> > > > +#define dsi_generic_write_seq(dsi, cmd, seq...) do { \
> > > > + static const u8 d[] = { seq }; \
> > > > + int ret; \
> > > > + ret = mipi_dsi_dcs_write(dsi, cmd, d, ARRAY_SIZE(d)); \
> > > > + if (ret < 0) \
> > > > + return ret; \
> > > > + } while (0)
> > > This macro return an error code if a write fails.
> > >
> > > > +
> > > > +static int xpp055c272_init_sequence(struct xpp055c272 *ctx)
> > > > +{
> > > > + struct mipi_dsi_device *dsi = to_mipi_dsi_device(ctx->dev);
> > > > + struct device *dev = ctx->dev;
> > > > + int ret;
> > > > +
> > > > + /*
> > > > + * Init sequence was supplied by the panel vendor without much
> > > > + * documentation.
> > > > + */
> > > > + dsi_generic_write_seq(dsi, XPP055C272_CMD_SETEXTC, 0xf1, 0x12, 0x83);
> > > But all uses of the macro here ignore the error.
> >
> > hmm, am I way off track here?
> >
> > dsi_generic_write_seq(dsi, XPP055C272_CMD_SETEXTC, 0xf1, 0x12, 0x83);
> > dsi_generic_write_seq(dsi, XPP055C272_CMD_SETMIPI,
> > 0x33, 0x81, 0x05, 0xf9, 0x0e, 0x0e, 0x00, 0x00,
> > 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x44, 0x25,
> > 0x00, 0x91, 0x0a, 0x00, 0x00, 0x02, 0x4f, 0x01,
> > 0x00, 0x00, 0x37);
> > ...
> >
> > should just expand to
> >
> > do {
> > static const u8 d[] = { 0xf1, 0x12, 0x83 };
> > int ret;
> > ret = mipi_dsi_dcs_write(dsi, XPP055C272_CMD_SETEXTC, d, ARRAY_SIZE(d));
> > if (ret < 0)
> > return ret;
> > } while (0)
> > do {
> > static const u8 d[] = { 0x33, 0x81, 0x05, 0xf9, 0x0e, 0x0e, 0x00, 0x00,
> > 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x44, 0x25,
> > 0x00, 0x91, 0x0a, 0x00, 0x00, 0x02, 0x4f, 0x01,
> > 0x00, 0x00, 0x37 };
> > int ret;
> > ret = mipi_dsi_dcs_write(dsi, XPP055C272_CMD_SETMIPI, d, ARRAY_SIZE(d));
> > if (ret < 0)
> > return ret;
> > } while (0)
> > ...
> >
> > so every write instance will actually return an error if it happens and not
> > continue on with the next init item.
> The idea was that if a write returned an error then do not even attempt
> more writes. So if a write fails we do not loose the original error
> code, assuming subsequent write would also fail.

Shouldn't the code above do exactly that? ... Because it's like

ret = dcs_write(...)
if (ret <0)
return ret;

So if any of the dcs_writes goes wrong it should just return the
error code from that write from the function and not try any more
writes. (or I'm blind and do not see something ;-) )


Heiko

> I have looked through all the panel drivers now, and the majority does
> not check if the write goes wrong.
> So following the pattern on the other panels you can also decide to just
> ignore the return value of mipi_dsi_dcs_write() rahter than trying to
> invent the check I tried to explain.
>
> Sam
>




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