linux-kernel - Re: [PATCH 07/12] drm/sun4i: sun6i_mipi

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Date:   Thu, 27 Sep 2018 23:15:50 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 07/12] drm/sun4i: sun6i_mipi_dsi: Fix TCON DRQ set bits

On Thu, Sep 27, 2018 at 10:28 PM Maxime Ripard
<maxime.ripard@...tlin.com> 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@...rulasolutions.com>
> > ---
> >  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?