linux-kernel - Re: [PATCH 1/2] ARM: tegra: Add Tegra20 host1x support

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Date:	Wed, 14 Nov 2012 11:54:06 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Terje Bergström <tbergstrom@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ARM: tegra: Add Tegra20 host1x support

On Wed, Nov 14, 2012 at 12:23:42PM +0200, Terje Bergström wrote:
> On 14.11.2012 10:49, Thierry Reding wrote:
> > Can you find out how the host1x clock is setup without this change? I
> > was told that freezes can occur when you try to access the registers
> > without the host1x clock being enabled. However, the host1x driver
> > should take care to properly setup the clock.
> > 
> > To find out if the non-running clock is the issue, can you try to patch
> > that line and make the final element true instead of false? That should
> > enable the clock on boot so that it should always be running.
> 
> I tried with fastboot and U-Boot, and whenever that line is there,
> kernel boot will halt at nvhost init. Same happens if I just change the
> false to true.
> 
> nvhost will enable the clock and disable as it need. Also, part of
> host1x initialization did proceed, but it ended up hanging after a few
> registers were initialized. So it's not a case of host1x being off, but
> host1x hanging after a while.
> 
> If I change this line to:
> 
>        { "host1x",     "pll_p",        216000000,      false },
> 
> it will also work properly. It looks like we have some problem with
> pll_c in Tegra20, or clock configuration with your patch. In Tegra30,
> pll_c with 144MHz seems to work fine, but on Tegra20, it doesn't.
> 
> In internal kernel, we use pll_c for host1x, so hardware shouldn't be
> the problem here.

I suppose that if things work properly without this line, then we should
probably just drop it. Stephen, any objections?

Thierry

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