Re: [linux-sunxi] [PATCH 3/3] Revert "drm/sun4i: dsi: Rework a bit the hblk calculation"

From: Icenowy Zheng <icenowy@aosc.io>
To: Jagan Teki <jagan@amarulasolutions.com>
Cc: David Airlie <airlied@linux.ie>,
	linux-sunxi <linux-sunxi@googlegroups.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Chen-Yu Tsai <wens@csie.org>, Maxime Ripard <mripard@kernel.org>,
	Daniel Vetter <daniel@ffwll.ch>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [linux-sunxi] [PATCH 3/3] Revert "drm/sun4i: dsi: Rework a bit the hblk calculation"
Date: Sun, 06 Oct 2019 22:44:25 +0800	[thread overview]
Message-ID: <58dc94b6371ab2f5b11b13ab707d73ab3fc4cc64.camel@aosc.io> (raw)
In-Reply-To: <CAMty3ZDW4XHyW+6XL_RSVHqTSk79-r749pa0n5e6VbUzowAsiw@mail.gmail.com>

在 2019-10-03四的 09:53 +0530，Jagan Teki写道：
> Hi Wens,
> 
> On Tue, Oct 1, 2019 at 1:34 PM Icenowy Zheng <icenowy@aosc.io> wrote:
> > This reverts commit 62e7511a4f4dcf07f753893d3424decd9466c98b.
> > 
> > This commit, although claimed as a refactor, in fact changed the
> > formula.
> > 
> > By expanding the original formula, we can find that the const 10 is
> > not
> > substracted, instead it's added to the value (because 10 is
> > negative
> > when calculating hsa, and hsa itself is negative when calculating
> > hblk).
> > This breaks the similar pattern to other formulas, so restoring the
> > original formula is more proper.
> > 
> > Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
> > ---
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 2d3e822a7739..cb5fd19c0d0d 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -577,14 +577,9 @@ static void sun6i_dsi_setup_timings(struct
> > sun6i_dsi *dsi,
> >                           (mode->hsync_start - mode->hdisplay) *
> > Bpp - HFP_PACKET_OVERHEAD);
> > 
> >                 /*
> > -                * The blanking is set using a sync event (4 bytes)
> > -                * and a blanking packet (4 bytes + payload + 2
> > -                * bytes). Its minimal size is therefore 10 bytes.
> > +                * hblk seems to be the line + porches length.
> >                  */
> > -#define HBLK_PACKET_OVERHEAD   10
> > -               hblk = max((unsigned int)HBLK_PACKET_OVERHEAD,
> > -                          (mode->htotal - (mode->hsync_end - mode-
> > >hsync_start)) * Bpp -
> > -                          HBLK_PACKET_OVERHEAD);
> > +               hblk = mode->htotal * Bpp - hsa;
> 
> The original formula is correct according to BSP [1] and work with my
> panels which I have tested before. May be the horizontal timings on
> panels you have leads to negative value.

Do you tested the same timing with BSP kernel?

It's quite difficult to get a negative value here, because the value is
quite big (includes mode->hdisplay * Bpp).

Strangely, only change the formula here back makes the timing
translated from FEX file works (tested on PineTab and PinePhone
production ver). The translation rule is from [1].

So I still insist on the patch because it's needed by experiment.

[1] http://linux-sunxi.org/LCD

> 
> [1] 
> https://github.com/ayufan-pine64/linux-pine64/blob/my-hacks-1.2-with-drm/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L919

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