On Mon, May 16, 2022 at 2:56 PM Joel Selvaraj <jo@xxxxxxxxxxx> wrote:
> On 13/05/22 03:21, Linus Walleij wrote:
> > On Fri, May 6, 2022 at 2:18 PM Joel Selvaraj <jo@xxxxxxxxxxx> wrote:
> >> +#define dsi_dcs_write_seq(dsi, seq...) do { \
> >> + static const u8 d[] = { seq }; \
> >> + int ret; \
> >> + ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d)); \
> >> + if (ret < 0) \
> >> + return ret; \
> >> + } while (0)
> >
> > First I don't see what the do {} while (0) buys you, just use
> > a basic block {}.
>
> The do {} while (0) in macro ensures there is a semicolon when it's
> used. With normal blocking, it would have issues with if conditions?
> I read about them here: https://stackoverflow.com/a/2381339
Hm that seems true, it enforces the semicolon ; at the end of the
statement which is nice. I suppose we should fix the other macro
as well.
Noralf added this ({}) form in 02dd95fe31693, so maybe he wants
to chip in.
> > Second look at mipi_dbi_command() in include/drm/drm_mipi_dbi.h
> > this is very similar.
>
> Does the ({..}) style blocking used in mipi_dbi_command help workaround
> the semicolon issue I mentioned above?
Nope. But add the rate limited error print please!
> > It's dubious that you always have dsi_dcs_write_seq()
> > followed by dsi_generic_write_seq().
> >
> > That means mipi_dsi_generic_write() followed by
> > mipi_dsi_dcs_write_buffer(). But if you look at these
> > commands in drivers/gpu/drm/drm_mipi_dsi.c
> > you see that they do the same thing!
>
> They almost do the same thing except for the msg.type values? Mostly the
> msg.type value is used to just check whether it's a long or short write
> in the msm dsi_host code. However, in mipi_dsi_create_packet function,
> the msg->type value is used to calculate packet->header[0] as follows:
>
> packet->header[0] = ((msg->channel & 0x3) << 6) | (msg->type & 0x3f);
>
> Wouldn't the difference between the mipi_dsi_dcs_write_buffer's and
> mipi_dsi_generic_write's msg.type values cause issue here?
>
> I tried using mipi_dsi_dcs_write_buffer for all commands and the panel
> worked fine, but I am not sure if it's correct to do so?
I think it's fine? The only issue would be if there is a DSI host controller
that only supports short writes, and in that case it should emulate
long writes by breaking long messages apart. (My amateur view at least.)
> > Lots of magic numbers. You don't have a datasheet do you?
> > So you could #define some of the magic?
>
> Unfortunately, I don't have a datasheet and the power on sequence is
> taken from downstream android dts. It works pretty well though. So I
> don't think I can #define any of these magic.
If you know which display controller the display is using (usually
Novatek nnnnn, Ilitek nnnn etc someting like that) there is often
a datasheet for the display controller available but the display per
se often obscures the display controller.
> > Doesn't it work to combine them into one call for each
> > pair?
> >> + dsi_dcs_write_seq(dsi, );
> >> + dsi_generic_write_seq(dsi, 0xff, 0x87, 0x19);
>
> By using a macro? We can... but I am not sure what (0x00, 0x80), (0x00,
> 0xa0),etc type of commands signify without the datasheet, so I am not
> sure what to name them in the macro and make any sensible meaning out of it.
I meant just sending dsi_generic_write_seq() with everything in
it:
dsi_generic_write_seq(dsi, 0x00, 0x80, 0xff, 0x87, 0x19);
Instead of two writes. Doesn't this work?
Yours,
Linus Walleij
