linux-kernel - Re: [PATCH v3 14/25] drm/sun4i: sun6i_mipi

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Date:   Mon, 29 Oct 2018 19:57:56 +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@...glegroups.com
Subject: Re: [PATCH v3 14/25] drm/sun4i: sun6i_mipi_dsi: Increase hfp packet overhead

On Mon, Oct 29, 2018 at 2:58 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Fri, Oct 26, 2018 at 08:13:33PM +0530, Jagan Teki wrote:
> > Increase the hfp packet overhead with another 10 bytes, the extra
> > 10 bytes(which is hblk packet overhead) is adding for hfp packet
> > overhead since hfp depends on hblk.
> >
> > This is truely as per BSP code from BPI-M64-bsp.
> > The real computation from BSP is
> > (in drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > dsi_hbp = (hbp-hspw)*dsi_pixel_bits[format]/8 - (4+2);
> > dsi_hact = x * dsi_pixel_bits[format]/8;
> > dsi_hblk = (ht-hspw)*dsi_pixel_bits[format]/8-(4+4+2);
> > dsi_hfp = dsi_hblk - (4+dsi_hact+2) - (4+dsi_hbp+2);
> >
> > Example,
> > u32 fmt = dsi_pixel_bits[format]/8;
> > => ((ht-hspw)*fmt - 10) - (6 + x * fmt) - (6 + (hbp-hspw)*fmt - 6)
> > => (ht - hspw - x - (hbp - hspw)) * fmt - 16
> > => (ht - x - hbp) * fmt - 16
> > => (ht - x - (timmings->hor_total_time - timmings->hor_front_porch - x)
> > * fmt - 16
> > => (timmings->hor_total_time - x - timmings->hor_total_time +
> > timmings->hor_front_porch + x) * fmt - 16
> > => timmings->hor_front_porch * fmt - 16
> >
> > So, increase the DSI hfp packet overhead by hblk packet overhead.
> >
> > Tested on 2-lane, 4-lane MIPI-DSI LCD panels.
> >
> > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > Tested-by: Jagan Teki <jagan@...rulasolutions.com>
> > ---
> > Changes for v3:
> > - new patch
> > Changes for v2:
> > - none
> >
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 22 +++++++++++++---------
> >  1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 6584b51736a9..20e330186b7f 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -461,7 +461,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> >  {
> >       struct mipi_dsi_device *device = dsi->device;
> >       unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;
> > -     u16 hbp, hfp, hsa, hblk_max, hblk, vblk;
> > +     u16 hbp, hfp_pkt_overhead, hfp, hsa, hblk_max, hblk, vblk;
> >       size_t bytes;
> >       u8 *buffer;
> >
> > @@ -484,14 +484,6 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> >       hbp = max((unsigned int)HBP_PACKET_OVERHEAD,
> >                 (mode->htotal - mode->hsync_end) * Bpp - HBP_PACKET_OVERHEAD);
> >
> > -     /*
> > -      * The frontporch is set using a blanking packet (4 bytes +
> > -      * payload + 2 bytes). Its minimal size is therefore 6 bytes
> > -      */
> > -#define HFP_PACKET_OVERHEAD  6
> > -     hfp = max((unsigned int)HFP_PACKET_OVERHEAD,
> > -               (mode->hsync_start - mode->hdisplay) * Bpp - HFP_PACKET_OVERHEAD);
> > -
> >       /*
> >        * hblk seems to be the line + porches length.
> >        * The blank is set using a blanking packet (4 bytes + 4 bytes +
> > @@ -502,6 +494,18 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> >       hblk_max -= HBLK_PACKET_OVERHEAD;
> >       hblk = max((unsigned int)HBLK_PACKET_OVERHEAD, hblk_max);
> >
> > +     /*
> > +      * The frontporch is set using a blanking packet (4 bytes +
> > +      * payload + 2 bytes). Its minimal size is therefore 6 bytes
> > +      *
> > +      * According to BSP code, extra 10 bytes(which is hblk packet overhead)
> > +      * is adding for hfp packet overhead since hfp depends on hblk.
>
> "According to the BSP code, another 10 bytes (the HBLK packet
> overhead) need to be added to the front porch overhead."
>
> How has this been verified? Since we have registers to set all the
> parameters, this seems kind of weird.

Verified based on the BSP calculation which I explained in commit
message and tested by validating these numbers with mainline vs bsp
code.