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

Giulio Benetti
2021-01-08T14:49:01Z

Hi Marjan,

On 1/8/21 10:32 AM, Marjan Pascolo wrote:
> Hi,

please don't top post, answer in-line as we do, and please use
plain-test instead of HTML. These are the standards in Mailing Lists(ML).

> Quote "
>
> I'm not really sure why we need the first patch of this series here?
> That patch only seem to undo what you did in patch 1
>
> "

Already answered to Maxime

>
> And another question (probably could be a stupid one):
>
> in "/[PATCH v2 2/2] drm/sun4i: tcon: improve DCLK polarity handling/" I
> see you deleted:
>
> - clk_set_phase(tcon->dclk, 0);
>
> Is safe to assume that phase register will be always set to 0?

We always assumed it is set to 0 by default.

>
> Or maybe will be safer manually set it to 0 in every condition to avoid
> surprises (dirt values due to previous condition)?

That would be a good idea, so something like this:

'''
int phase = 0;

if (info->bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
phase = 240;

clk_set_phase(tcon->dclk, phase);
'''

because now DRM_BUS_FLAG_PIXDATA_SAMPLE_ and DRM_BUS_FLAG_PIXDATA_DRIVE_
are exclusive, while before not.

But then if bit 26 solution works everything gets easier.

Best Regards
Giulio

>
> Marjan
>
> Il 08/01/2021 10:23, Maxime Ripard ha scritto:
>> Hi,
>>
>> Thanks for those patches
>>
>> On Thu, Jan 07, 2021 at 03:30:32AM +0100, Giulio Benetti wrote:
>>> From: Giulio Benetti<giulio.benetti@micronovasrl.com>
>>>
>>> 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@cerno.tech>
>> Suggested-by would be nice here :)
>>
>>> Signed-off-by: Giulio Benetti<giulio.benetti@micronovasrl.com>
>>> ---
>>> 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?
>> That patch only seem to undo what you did in patch 1
>>
>> Maxime