Re: [PATCH v3 12/25] drm/sun4i: sun6i_mipi_dsi: Add DSI hblk packet overhead

From: Jagan Teki <jagan@amarulasolutions.com>
To: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Chen-Yu Tsai <wens@csie.org>, Icenowy Zheng <icenowy@aosc.io>,
	Jernej Skrabec <jernej.skrabec@siol.net>,
	Vasily Khoruzhick <anarsoul@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	David Airlie <airlied@linux.ie>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Michael Trimarchi <michael@amarulasolutions.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	devicetree <devicetree@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-sunxi@googlegroups.com
Subject: Re: [PATCH v3 12/25] drm/sun4i: sun6i_mipi_dsi: Add DSI hblk packet overhead
Date: Mon, 29 Oct 2018 19:56:27 +0530	[thread overview]
Message-ID: <CAMty3ZBHU5eXRLLJmUroLgSKcF6O9gHOHRM1XBnt9_Lp7B8rEA@mail.gmail.com> (raw)
In-Reply-To: <20181029092227.mdxgvg5aqzh22j72@flea>

On Mon, Oct 29, 2018 at 2:52 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> On Fri, Oct 26, 2018 at 08:13:31PM +0530, Jagan Teki wrote:
> > Add 10 bytes packet overhead for hblk where blank is set using
> > a blanking packet like (4 bytes + 4 bytes + payload + 2 bytes)
> >
> > This is according to BSP code from BPI-M64-bsp
> > (in drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > dsi_hblk = (ht-hspw)*dsi_pixel_bits[format]/8-(4+4+2);
> >
> > So, add 10 bytes packet overhead for DSI hblk.
> >
> > Tested on 2-lane, 4-lane MIPI-DSI LCD panels.
> >
> > Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> > Tested-by: Jagan Teki <jagan@amarulasolutions.com>
> > ---
> > Changes for v3:
> > - new patch
> > Changes for v2:
> > - none
> >
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 596e560263bf..cf42be1f1ba1 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, vblk;
> > +     u16 hbp, hfp, hsa, hblk_max, hblk, vblk;
> >       size_t bytes;
> >       u8 *buffer;
> >
> > @@ -494,8 +494,13 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> >
> >       /*
> >        * hblk seems to be the line + porches length.
> > +      * The blank is set using a blanking packet (4 bytes + 4 bytes +
> > +      * payload + 2 bytes). So minimal size is 10 bytes
> >        */
> > -     hblk = (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp;
> > +#define HBLK_PACKET_OVERHEAD 10
> > +     hblk_max = (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp;
> > +     hblk_max -= HBLK_PACKET_OVERHEAD;
> > +     hblk = max((unsigned int)HBLK_PACKET_OVERHEAD, hblk_max);
>
> I'd rather use the same convention than the other assignments done
> before in that function.

Yes, old code did use hsa. but it's added 10 bytes packet head instead
of subtracting it.

hblk = mode->htotal * Bpp - hsa;
=> mode->htotal * Bpp - (mode->hsync_end - mode->hsync_start) * Bpp -
HSA_PACKET_OVERHEAD);
=> (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp +
HSA_PACKET_OVERHEAD;

And it should be
(mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp -
HSA_PACKET_OVERHEAD;

This patch is simply doing the same by explicitly adding packet over
ahead macro, which again used in hfp.