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

From: Marjan Pascolo <marjan.pascolo@trexom.it>
To: Maxime Ripard <maxime@cerno.tech>,
	Giulio Benetti <giulio.benetti@benettiengineering.com>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>,
	airlied@linux.ie, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, wens@csie.org,
	treding@nvidia.com,
	Giulio Benetti <giulio.benetti@micronovasrl.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 2/2] drm/sun4i: tcon: improve DCLK polarity handling
Date: Fri, 8 Jan 2021 10:32:41 +0100	[thread overview]
Message-ID: <00f21d15-7a88-2d01-dd48-dc49e9295e34@trexom.it> (raw)
In-Reply-To: <20210108092355.7p5uakxt7lpdu3bn@gilmour>

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Hi,

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

"

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?

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

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

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