On Thu, 25 Apr 2024 at 01:15, Hsin-Yi Wang <hsi...@google.com> wrote:
>
> On Wed, Apr 24, 2024 at 2:49 PM Dmitry Baryshkov
> <dmitry.barysh...@linaro.org> wrote:
> >
> > On Thu, 25 Apr 2024 at 00:04, Doug Anderson <diand...@google.com> wrote:
> > >
> > > Hi,
> > >
> > > On Tue, Apr 23, 2024 at 2:20 PM Dmitry Baryshkov
> > > <dmitry.barysh...@linaro.org> wrote:
> > > >
> > > > On Tue, Apr 23, 2024 at 01:41:59PM -0700, Doug Anderson wrote:
> > > > > Hi,
> > > > >
> > > > > On Tue, Apr 23, 2024 at 11:10 AM Hsin-Yi Wang <hsi...@google.com>
> > > > > wrote:
> > > > > >
> > > > > > > > > > +#define _INIT_DCS_CMD(...) { \
> > > > > > > > > > + .type = INIT_DCS_CMD, \
> > > > > > > > > > + .len = sizeof((char[]){__VA_ARGS__}), \
> > > > > > > > > > + .data = (char[]){__VA_ARGS__} }
> > > > > > > > > > +
> > > > > > > > > > +#define _INIT_DELAY_CMD(...) { \
> > > > > > > > > > + .type = DELAY_CMD,\
> > > > > > > > > > + .len = sizeof((char[]){__VA_ARGS__}), \
> > > > > > > > > > + .data = (char[]){__VA_ARGS__} }
> > > > > > > > >
> > > > > > > > > This is the third panel driver using the same appoach. Can
> > > > > > > > > you use
> > > > > > > > > mipi_dsi_generic_write_seq() instead of the huge table? Or if
> > > > > > > > > you prefer
> > > > > > > > > the table, we should extract this framework to a common
> > > > > > > > > helper.
> > > > > > > > > (my preference is shifted towards
> > > > > > > > > mipi_dsi_generic_write_seq()).
> > > > > > > > >
> > > > > > > > The drawback of mipi_dsi_generic_write_seq() is that it can
> > > > > > > > cause the
> > > > > > > > kernel size grows a lot since every sequence will be expanded.
> > > > > > > >
> > > > > > > > Similar discussion in here:
> > > > > > > > https://lore.kernel.org/dri-devel/CAD=FV=Wju3WS45=EpXMUg7FjYDh3-=mvm_js7tf1tsaazbb...@mail.gmail.com/
> > > > > > > >
> > > > > > > > This patch would increase the module size from 157K to 572K.
> > > > > > > > scripts/bloat-o-meter shows chg +235.95%.
> > > > > > > >
> > > > > > > > So maybe the common helper is better regarding the kernel
> > > > > > > > module size?
> > > > > > >
> > > > > > > Yes, let's get a framework done in a useful way.
> > > > > > > I'd say, drop the _INIT_DELAY_CMD. msleep() and usleep_range()
> > > > > > > should be
> > > > > > > used instead (and it's up to the developer to select correct delay
> > > > > > > function).
> > > > > > >
> > > > > > > >
> > > > > > > > > > +
> > > > > > > > > > +static const struct panel_init_cmd
> > > > > > > > > > kingdisplay_kd101ne3_init_cmd[] = {
> > > > > > > > > > + _INIT_DELAY_CMD(50),
> > > > > > > > > > + _INIT_DCS_CMD(0xE0, 0x00),
> > > > > > >
> > > > > > > [skipped the body of the table]
> > > > > > >
> > > > > > > > > > + _INIT_DCS_CMD(0x0E, 0x48),
> > > > > > > > > > +
> > > > > > > > > > + _INIT_DCS_CMD(0xE0, 0x00),
> > > > > > >
> > > > > > > > > > + _INIT_DCS_CMD(0X11),
> > > > > > >
> > > > > > > Also, at least this is mipi_dsi_dcs_exit_sleep_mode().
> > > > > > >
> > > > > > > > > > + /* T6: 120ms */
> > > > > > > > > > + _INIT_DELAY_CMD(120),
> > > > > > > > > > + _INIT_DCS_CMD(0X29),
> > > > > > >
> > > > > > > And this is mipi_dsi_dcs_set_display_on().
> > > > > > >
> > > > > > > Having a single table enourages people to put known commands into
> > > > > > > the
> > > > > > > table, the practice that must be frowned upon and forbidden.
> > > > > > >
> > > > > > > We have functions for some of the standard DCS commands. So, maybe
> > > > > > > instead of adding a single-table based approach we can improve
> > > > > > > mipi_dsi_generic_write_seq() to reduce the bloat. E.g. by moving
> > > > > > > the
> > > > > > > error handling to a common part of enable() / prepare() function.
> > > > > > >
> > > > > >
> > > > > > For this panel, I think it can also refer to how
> > > > > > panel-kingdisplay-kd097d04.c does. Create the table for init cmd
> > > > > > data,
> > > > > > not what operation to use, and use mipi_dsi_generic_write_seq() when
> > > > > > looping through the table.
> > > > >
> > > > > Even more similar discussion:
> > > > >
> > > > > https://lore.kernel.org/r/CAD=FV=ugdbnvamjzwsovxybgikqcvw9jsrtbxhvg8_97ype...@mail.gmail.com
> > > >
> > > > It seems I skipped that thread.
> > > >
> > > > I'd still suggest a code-based solution compared to table-based one, for
> > > > the reasons I've outlined before. Having a tables puts a pressure on the
> > > > developer to put commands there for which we already have a
> > > > command-specific function.
> > >
> > > The problem is that with these panels that need big init sequences the
> > > code based solution is _a lot_ bigger. If it were a few bytes or a
> > > 1-2KB then fine, but when Hsin-Yi measured Linus W's attempt to move
> > > from a table to code it was 100K difference in code [1]. I would also
> > > say that having these long init sequences done as separate commands
> > > encourages people to skip checking the return values of each of the
> > > transfer functions and I don't love that idea.
> > >
> > > It would be ideal if these panels didn't need these long init
> > > sequences, but I don't have any inside knowledge here saying that they
> > > could be removed. So assume we can't get rid of the init sequences it
> > > feels like we have to find some way to make the tables work for at
> > > least the large chunks of init code and encourage people to make the
> > > tables readable...
> >
> >
> > I did a quick check on the boe-tv101wum-nl6 driver by converting the
> > writes to use the following macro:
> >
> > #define mipi_dsi_dcs_write_cmd_seq(dsi, cmd, seq...)
> > \
> > do {
> > \
> > static const u8 d[] = { cmd, seq }; \
> > ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d)); \
> > if (ret < 0)
> > \
> > goto err;
> > \
> > } while (0)
> >
> > And then at the end of the init funciton having
> >
> > err:
> > dev_err(panel->dev,
> > "failed to write command %d\n", ret);
> > return ret;
> > }
> >
>
> I'm not sure about the coding style rule here, would it be considered
> unclear that caller of mipi_dsi_dcs_write_cmd_seq() needs to have err
> block, but the block may not be directly used in that caller and is
> only jumped from the macro?
I'm also not sure here. It was a quick and dirty test.
We might as well do something like
ret = mipi_dsi_dcs_write_cmd_seq(dsi, ...);
if (ret)
goto err;
all over the place.
>
>
> > Size comparison:
> > text data bss dec hex filename
> > before
> > 34109 10410 18 44537 adf9
> > ../build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o
> > making init data const
> > 44359 184 0 44543 adff
> > ../build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o
> > with new macros
> > 44353 184 0 44537 adf9
> > ../build-64/drivers/gpu/drm/panel/panel-boe-tv101wum-nl6.o
> >
> > As you can see, there is literally no size difference with this macro in
> > place.
> > The only drawback is that the init stops on the first write rather
> > than going through the sequence.
> >
> > WDYT? I can turn this into a proper patch if you think this makes sense.
> >
> > >
> > >
> > > [1]
> > > https://lore.kernel.org/r/CAD=FV=UFa_AoJQvUT3BTiRs19WCA2xLVeQOU=+nyu_hae0_...@mail.gmail.com
> >
> >
> >
> > --
> > With best wishes
> > Dmitry
--
With best wishes
Dmitry
