linux-kernel - Re: [Intel-gfx] [PATCH 6/7] drm/i915: Disable FDI RX before FDI TX

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Message-ID: <86393lunb2.fsf@miki.keithp.com>
Date:	Fri, 17 Aug 2012 16:10:57 -0700
From:	Keith Packard <keithp@...thp.com>
To:	"Lespiau\, Damien" <damien.lespiau@...el.com>
Cc:	intel-gfx@...ts.freedesktop.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 6/7] drm/i915: Disable FDI RX before FDI TX

"Lespiau, Damien" <damien.lespiau@...el.com> writes:

> I can't see anything in the docs about an order requirement for those.

Right, the docs don't say anything, which is a bit disconcerting.

> Not sure why the other way does not make sense. Somehow disabling TX
> before RX makes some sense to me (TX enabled without a ready RX looks
> weird?, no data should flow as the pipe is shutdown at that point
> anyway). Maybe it just does not matter?

And here I figured disabling RX before TX made more sense -- otherwise
the receiver wouldn't be seeing anything. In other areas of the driver,
we're careful to disable receivers before senders (disable CRTC before
PLL, etc).

> Another detail is that disabling the PLLs seem to have an order in the
> disabling sequence, TX, then RX.
>
> I.  Disable CPU FDI Transmitter PLL
> II. Disable PCH FDI Receiver PLL

That ordering doesn't matter as the FDI receiver and transmitter are
both disabled by that point, so they aren't talking at all.

-- 
keith.packard@...el.com

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