linux-kernel - Re: [PATCH 2/2] drm/sun4i: Handle DRM_MODE_FLAG_**SYNC

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Message-ID: <20180205142155.vgd2olchbwzm6a7x@flea>
Date:   Mon, 5 Feb 2018 15:21:55 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Giulio Benetti <giulio.benetti@...ronovasrl.com>
Cc:     airlied@...ux.ie, wens@...e.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/sun4i: Handle DRM_MODE_FLAG_**SYNC_POSITIVE
 correctly

On Thu, Feb 01, 2018 at 05:09:33PM +0100, Giulio Benetti wrote:
> Il 01/02/2018 11:14, Maxime Ripard ha scritto:
> > On Sat, Jan 27, 2018 at 11:07:09PM +0100, Giulio Benetti wrote:
> > > > > > > I don't really know what the polarity of D0 would be just by
> > > > > > > judging at that capture, but we would have noticed if the colors
> > > > > > > were inverted for quite some time now.
> > > > > > 
> > > > > > D0-D23 are correct.
> > > > > > 
> > > > > > With that capture, I mean to show you instead dclk is inverted, as
> > > > > > dclk samples D0 on falling edge.
> > > > > 
> > > > > Ah right, DCLK being the first channel?
> > > > 
> > > > Yes, sorry I didn't place a label on channels
> > > > 
> > > > > 
> > > > > > So 0 is NEGEDGE and 1 is POSEDGE(1/3 of clock phase).
> > > > > > 1/3 clock phase seems enough to me to be considered POSEDGE,
> > > > > > 2/3 instead risks to go too much to the right of D0(even if it
> > > > > > could work).
> > > > > 
> > > > > Do you have captures with both settings?
> > > > 
> > > > Not now, but asap I'm going to take.
> > > 
> > > Here we are:
> > > 1/3 phase: https://pasteboard.co/H4VehON.png
> > > 2/3 phase: https://pasteboard.co/H4Veq8a.png
> > > 
> > > Yellow: D0
> > > Blue: DCLK
> > > 
> > > As you can see:
> > > 1/3 phase has DCLK rising edge almost in the middle of D0
> > > 2/3 phase has DCLK rising edge that comes too late
> > > 
> > > I would go for "1/3 phase" for Rising edge and "normal phase" for
> > > Falling edge.
> > > 
> > > What do you think?
> > 
> > It seems fair. This need a whole lot of comments though :)
> 
> Yes, then, do I proceed resubmitting both corrected patches with corrected
> commit logs?

Yes, please.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com

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