linux-kernel - Re: [PATCH 1/11] ARM: tegra: add function to control the GPU rail clamp

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Date:	Tue, 30 Dec 2014 17:42:32 +0100
From:	Lucas Stach <dev@...xeye.de>
To:	Vince Hsu <vinceh@...dia.com>
Cc:	thierry.reding@...il.com, swarren@...dotorg.org, gnurou@...il.com,
	bskeggs@...hat.com, martin.peres@...e.fr, seven@...rod-online.com,
	samuel.pitoiset@...il.com, nouveau@...ts.freedesktop.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/11] ARM: tegra: add function to control the GPU rail
 clamp

Am Montag, den 29.12.2014, 10:49 +0800 schrieb Vince Hsu:

[...]

> >> That's a read fence to assure the post of the previous writes through
> >> Tegra interconnect. (copy-paster from
> >> https://android.googlesource.com/kernel/tegra.git/+/28b107dcb3aa122de8e94e48af548140d519298f)
> > I see what it does, the question is more about why this is needed.
> > What is the Tegra interconnect? According to the TRM the Tegra contains
> > some standard AXI <-> AHB <-> APB bridges. That a read is needed to
> > assure the write is posted to the APB bus seems to imply that there is
> > some write buffering in one of those bridges. Can we get this documented
> > somewhere?
> The TRM does mention a read after the write. Check the section 32.2.2.3.
> 
Unfortunately this doesn't seem to be included in the public TRM. It
would be nice if this could be documented either in the next version of
the TRM or as a public Appnote.

Thanks,
Lucas


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