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

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Date:	Mon, 5 Jan 2015 14:55:38 +0800
From:	Vince Hsu <vinceh@...dia.com>
To:	Lucas Stach <dev@...xeye.de>
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


On 12/31/2014 12:42 AM, Lucas Stach wrote:
> 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.
>
It should be in the latest public TRM. Could you check again?

Thanks,
Vince

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