Re: [PATCH v9 2/5] drm/sun4i: sun6i_mipi_dsi: Fix TCON DRQ set bits

[Maxime Ripard <maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>]

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On Thu, Mar 07, 2019 at 05:49:07PM +0530, Jagan Teki wrote:
> On Mon, Mar 4, 2019 at 9:13 PM Maxime Ripard <maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org> wrote:
> >
> > On Sun, Mar 03, 2019 at 11:05:24PM +0530, Jagan Teki wrote:
> > > TCON DRQ for non-burst DSI mode can computed based on horizontal
> > > front porch value, but the current driver trying to include sync
> > > timings along with front porch resulting wrong drq.
> > >
> > > This patch is trying to update the drq by subtracting hsync_start
> > > with hdisplay, which is horizontal front porch.
> > >
> > > Current code:
> > > ------------
> > > mode->hsync_end - mode->hdisplay => horizontal front porch + sync
> > >
> > > With this patch:
> > > ----------------
> > > mode->hsync_start - mode->hdisplay => horizontal front porch
> > >
> > > BSP code form BPI-M64-bsp is computing TCON DRQ set bits
> > > for non-burts as (from linux-sunxi/
> > > drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > >
> > > => panel->lcd_ht -    panel->lcd_x - panel->lcd_hbp
> > > => (timmings->hor_front_porch + panel->lcd_hbp + panel->lcd_x)
> >                                   ^ + sync length +
> > >    - panel->lcd_x - panel->hbp
> > > => timmings->hor_front_porch
> >                                ^ + sync
> > > => mode->hsync_start - mode->hdisplay
> >
> > s/hsync_start/hsync_end/
> 
> No, it should be front porch so it is hsync_start. This change is
> trying to update DRQ set to use front porch and above evaluation from
> BSP, result the same front front porch
> 
> Current driver has hsync_end - hdisplay which is not front porch
> timing (it is adding extra sync timing).

It would be if you considered that the back porch actually was the
back porch plus the sync length. I have found no such evidence, quite
the opposite actually, everything seems to point at the fact that
unlike the TCON, the DSI block uses the back porch as only the back
porch.


> I believe this is something similar like fixed patches for VBP, HBLK
> timings.
>
> > Did you encounter any panel where this was fixing something? If so,
> > which one, and what is the matching timings and / or datasheet?
> 
> W/O this change Bananapi  s070wv20 panel has issue on striped lines on
> the panel[1] and timings are
> 
> static const struct drm_display_mode s070wv20_default_mode = {
>         .clock = 30000,
>         .vrefresh = 60,
> 
>         .hdisplay = 800,
>         .hsync_start = 800 + 40,
>         .hsync_end = 800 + 40 + 48,
>         .htotal = 800 + 40 + 48 + 40,
> 
>         .vdisplay = 480,
>         .vsync_start = 480 + 13,
>         .vsync_end = 480 + 13 + 3,
>         .vtotal = 480 + 13 + 3 + 29,
> };
> 
> Which is similar like in panel-simple "bananapi,s070wv20-ct16"
> 
> Here is the DSI panel patches and sequence:
> [pixel clock is 30Mhz] https://patchwork.kernel.org/patch/10680331/
> https://github.com/yesnoandor/x300/blob/master/kernel/arch/arm/boot/dts/erobbing/x300/x300.dtsi#L81
> https://github.com/wxzed/Raspberry_5MIPI_Display/blob/master/I2C_Slave/USER/main.c#L15
> https://github.com/eliot-shao/qcom/blob/master/icn6211_cxn0102/kernel/drivers/video/msm/mdss/mdss_i2c_interface.c#L152

What are those supposed to be? It doesn't look like timings but rather initialization sequences

> matches timings for
> https://github.com/eliot-shao/qcom/blob/master/icn6211_cxn0102/kernel/arch/arm/boot/dts/qcom/dsi-mipi-2-rgb_1280p_video.dtsi#L20

That's not even the same resolution..

> https://github.com/zestroly/micromat/blob/master/test/raspberry/ICN6211.cpp#L169

And this isn't a set of timings either.

> Attached is panel datasheet.

Which is for an RGB panel... not a MIPI-DSI one.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com