linux-kernel - Re: [PATCH v2 04/12] drm/sun4i: sun6i_mipi_dsi: Simplify drq set to support all modes

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Date:   Mon, 19 Nov 2018 16:52:17 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        TL Lim <tllim@...e64.org>, linux-sunxi@...glegroups.com,
        linux-amarula@...rulasolutions.com
Subject: Re: [PATCH v2 04/12] drm/sun4i: sun6i_mipi_dsi: Simplify drq set to
 support all modes

On Mon, Nov 19, 2018 at 2:02 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Fri, Nov 16, 2018 at 10:09:08PM +0530, Jagan Teki wrote:
> > Allwinner MIPI DSI DRQ set value can be varied with respective
> > video modes.
> > - burst mode the set value is always 0
> > - video modes whose front porch greater than 20, the set value
> >   can be computed based front porch and bpp.
> > - video modes whose front porch is not greater than 20, the set value
> >   is simply 0
> >
> > This patch simplifies existing drq set value code by grouping
> > into sun6i_dsi_get_drq and support all video modes.
> >
> > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 38 ++++++++++++++++----------
> >  1 file changed, 23 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index efd08bfd0cb8..d60955880c43 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -363,6 +363,26 @@ static void sun6i_dsi_inst_init(struct sun6i_dsi *dsi,
> >                    SUN6I_DSI_INST_JUMP_CFG_NUM(1));
> >  };
> >
> > +static int sun6i_dsi_get_drq(struct sun6i_dsi *dsi,
> > +                           struct drm_display_mode *mode)
> > +{
> > +     struct mipi_dsi_device *device = dsi->device;
> > +     int drq = 0;
>
> So, here, you declaring a variable called drq, set to 0.
>
> > +     if (device->mode_flags & MIPI_DSI_MODE_VIDEO_BURST)
> > +             return drq;
>
> That you return here. You could just return 0, to be clearer.
>
> > +     if ((mode->hsync_start - mode->hdisplay) > 20) {
> > +             /* Maaaaaagic */
> > +             u16 drq = (mode->hsync_start - mode->hdisplay) - 20;
>
> You re-declare a variable with the same name here, but a different
> type....
>
> > +             drq *= mipi_dsi_pixel_format_to_bpp(device->format);
> > +             drq /= 32;
> > +     }
> > +
> > +     return drq;
>
> And then return the first one? How is that even working?

Will fix this.

>
> > +
> >  static u16 sun6i_dsi_get_timings_vblk(struct sun6i_dsi *dsi,
> >                                     struct drm_display_mode *mode, u16 hblk)
> >  {
> > @@ -478,21 +498,9 @@ static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
> >  static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
> >                                 struct drm_display_mode *mode)
> >  {
> > -     struct mipi_dsi_device *device = dsi->device;
> > -     u32 val = 0;
> > -
> > -     if ((mode->hsync_start - mode->hdisplay) > 20) {
> > -             /* Maaaaaagic */
> > -             u16 drq = (mode->hsync_start - mode->hdisplay) - 20;
> > -
> > -             drq *= mipi_dsi_pixel_format_to_bpp(device->format);
> > -             drq /= 32;
> > -
> > -             val = (SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> > -                    SUN6I_DSI_TCON_DRQ_SET(drq));
> > -     }
> > -
> > -     regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG, val);
> > +     regmap_write(dsi->regs, SUN6I_DSI_TCON_DRQ_REG,
> > +                  SUN6I_DSI_TCON_DRQ_ENABLE_MODE |
> > +                  SUN6I_DSI_TCON_DRQ_SET(sun6i_dsi_get_drq(dsi, mode)));
>
> On top of that, you now enable the DRQ stuff all the time, while it

Earlier the val value is ENABLE_MODE ORed with drq value. for the
condition drq is computed in if block otherwise the val is 0.
So as I explained in commit message the drq value is 0
- for video modes whose front porch is not greater than 20 and
- for burst mode the val

ie reason I mode it common.