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

[Maxime Ripard]

On Wed, Oct 03, 2018 at 08:52:06AM +0530, Jagan Teki wrote:
> 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.

And this should be in your commit log as well.

Maxime

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

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