Re: [PATCH v2 2/2] drm/sun4i: tcon: improve DCLK polarity handling

[Giulio Benetti]

Hi,

On 1/8/21 10:23 AM, Maxime Ripard wrote:
> Hi,
>
> Thanks for those patches
>
> On Thu, Jan 07, 2021 at 03:30:32AM +0100, Giulio Benetti wrote:
> > From: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
> >
> > It turned out(Maxime suggestion) that bit 26 of SUN4I_TCON0_IO_POL_REG is
> > dedicated to invert DCLK polarity and this makes thing really easier than
> > before. So let's handle DCLK polarity by adding
> > SUN4I_TCON0_IO_POL_DCLK_POSITIVE as bit 26 and activating according to
> > bus_flags the same way is done for all the other signals.
> >
> > Cc: Maxime Ripard <maxime@xxxxxxxxxx>
>
> Suggested-by would be nice here :)

Ok, didn't know about this tag

> > Signed-off-by: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/sun4i/sun4i_tcon.c | 20 +-------------------
> >   drivers/gpu/drm/sun4i/sun4i_tcon.h |  1 +
> >   2 files changed, 2 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > index 52598bb0fb0b..30171ccd87e5 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > @@ -569,26 +569,8 @@ static void sun4i_tcon0_mode_set_rgb(struct sun4i_tcon *tcon,
> >   	if (info->bus_flags & DRM_BUS_FLAG_DE_LOW)
> >   		val |= SUN4I_TCON0_IO_POL_DE_NEGATIVE;
> >   
> > -	/*
> > -	 * On A20 and similar SoCs, the only way to achieve Positive Edge
> > -	 * (Rising Edge), is setting dclk clock phase to 2/3(240°).
> > -	 * By default TCON works in Negative Edge(Falling Edge),
> > -	 * this is why phase is set to 0 in that case.
> > -	 * Unfortunately there's no way to logically invert dclk through
> > -	 * IO_POL register.
> > -	 * The only acceptable way to work, triple checked with scope,
> > -	 * is using clock phase set to 0° for Negative Edge and set to 240°
> > -	 * for Positive Edge.
> > -	 * On A33 and similar SoCs there would be a 90° phase option,
> > -	 * but it divides also dclk by 2.
> > -	 * Following code is a way to avoid quirks all around TCON
> > -	 * and DOTCLOCK drivers.
> > -	 */
> >   	if (info->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_POSEDGE)
> > -		clk_set_phase(tcon->dclk, 0);
> > -
> > -	if (info->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
> > -		clk_set_phase(tcon->dclk, 240);
> > +		val |= SUN4I_TCON0_IO_POL_DCLK_POSITIVE;
>
> I'm not really sure why we need the first patch of this series here?

The idea was to have 2 for testing, 1st one is already applicable, while 
the other must be tested, but I can send only one with no problem.

> That patch only seem to undo what you did in patch 1

No, it doesn't, the 2nd one change the way it achieve the same thing, 
because the 1st swap DCLK phase, while the 2nd uses the IO_POL bit to 
set IO polarity according to bus_flags.

Best Regards
--
Giulio Benetti
Benetti Engineering sas