Re: [linux-sunxi] Re: [PATCH 07/12] drm/sun4i: sun6i_mipi_dsi: Fix TCON DRQ set bits

[Jagan Teki]

On Tuesday 02 October 2018 06:50 PM, Maxime Ripard wrote:
> On Thu, Sep 27, 2018 at 11:15:50PM +0530, Jagan Teki wrote:
> > On Thu, Sep 27, 2018 at 10:28 PM Maxime Ripard
> > <maxime.ripard@xxxxxxxxxxx> wrote:
> > > On Thu, Sep 27, 2018 at 05:18:45PM +0530, Jagan Teki wrote:
> > > > TCON DRQ set bits for non-burst DSI mode can computed via
> > > > horizontal front porch instead of front porch + sync timings.
> > > >
> > > > Since there no documentation for TCON_DRQ_REG(0x7c) register
> > > > this change is taken as reference from BPI-M64-bsp.
> > >
> > > Detailing more what the issue is would be great.
> > >
> > > > Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >   drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
> > > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > index 599284971ab6..9918fdb990ff 100644
> > > > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > @@ -367,9 +367,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
> > > >        struct mipi_dsi_device *device = dsi->device;
> > > >        u32 val = 0;
> > >
> > > The computation here is in the A64 driver:
> > >
> > > if ((panel->lcd_ht - panel->lcd_x - panel->lcd_hbp) < 21) {
> > >          dsi_dev[sel]->dsi_tcon_drq.bits.drq_mode = 0;
> > > } else {
> > >          dsi_dev[sel]->dsi_tcon_drq.bits.drq_set =
> > >                  (panel->lcd_ht-panel->lcd_x-panel->lcd_hbp-20) *
> > >                  dsi_pixel_bits[panel->lcd_dsi_format]/(8*4);
> > > }
> > >
> > > It is testing that the sync + front porch is smaller than 21, and
> > > otherwise sets the drq.
> > >
> > > > -     if ((mode->hsync_end - mode->hdisplay) > 20) {
> > >
> > > My code here is testing that the difference between hsync_end and
> > > hdisplay is superior to 20, and sets the DRQ if true. The condition is
> > > reversed, but otherwise, that difference is the front porch plus the
> > > sync length.
> >
> > True, I understand this, but does drq setting here is specific to SoC?
> > I thought of finding DRQ in A31 BSP but I couldn't find the code. do
> > you have bsp somewhere in github?
> >
> > > > +     if ((mode->hsync_start - mode->hdisplay) > 20) {
> > >
> > > However, you are testing for just the front porch, unlike what your
> > > commit log is saying, and unlike what allwinner's code is saying. So
> > > this deserves some explanation.
> >
> > but A64 is doing this, do you think it's completely A64 specific or
> > testing panel with front porch drq?
>
> See the above code excerpt:
> panel->lcd_ht - panel->lcd_x - panel->lcd_hbp
>
> This is hsync + front porch. Not the sole front porch. So no, it's not
> doing this.

=> panel->lcd_ht - panel->lcd_x - panel->lcd_hbp

from drivers/video/sunxi/disp2/disp/de/disp_lcd.c
timmings->hor_front_porch= panel_info->lcd_ht-panel_info->lcd_hbp - 
panel_info->lcd_x;

=> (timmings->hor_front_porch + panel->lcd_hbp + panel->lcd_x) - 
panel->lcd_x - panel->hbp
=> timmings->hor_front_porch
=> mode->hsync_start - mode->hdisplay

This is simply a front porch.