linux-kernel - Re: [PATCH v2 2/3] ARM: tegra: Add SMMU enabler in AHB

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Message-ID: <20120424.160319.1903472399760352200.hdoyu@nvidia.com>
Date:	Tue, 24 Apr 2012 15:03:19 +0200
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"balbi@...com" <balbi@...com>
CC:	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"ccross@...roid.com" <ccross@...roid.com>,
	"olof@...om.net" <olof@...om.net>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"tony@...mide.com" <tony@...mide.com>,
	"hsweeten@...ionengravers.com" <hsweeten@...ionengravers.com>,
	"jamie@...ieiles.com" <jamie@...ieiles.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] ARM: tegra: Add SMMU enabler in AHB

From: Felipe Balbi <balbi@...com>
Subject: Re: [PATCH v2 2/3] ARM: tegra: Add SMMU enabler in AHB
Date: Tue, 24 Apr 2012 14:41:18 +0200
Message-ID: <20120424124115.GL8444@...en.pp.htv.fi>

> * PGP Signed by an unknown key
> 
> On Tue, Apr 24, 2012 at 02:39:30PM +0200, Hiroshi Doyu wrote:
> > From: Felipe Balbi <balbi@...com>
> > Subject: Re: [PATCH v2 2/3] ARM: tegra: Add SMMU enabler in AHB
> > Date: Tue, 24 Apr 2012 14:32:52 +0200
> > Message-ID: <20120424123248.GG8444@...en.pp.htv.fi>
> > 
> > > > Old Signed by an unknown key
> > > 
> > > Hi,
> > > 
> > > On Tue, Apr 24, 2012 at 03:05:15PM +0300, Hiroshi DOYU wrote:
> > > > @@ -95,6 +98,21 @@ static inline void gizmo_writel(unsigned long value, unsigned long offset)
> > > >  	writel(value, tegra_ahb->regs + offset);
> > > >  }
> > > >  
> > > > +#ifdef CONFIG_ARCH_TEGRA_3x_SOC
> > > > +
> > > > +void tegra_ahb_enable_smmu(void)
> > > > +{
> > > > +	unsigned long val;
> > > > +
> > > > +	val = gizmo_readl(AHB_ARBITRATION_XBAR_CTRL);
> > > > +	val |= AHB_ARBITRATION_XBAR_CTRL_SMMU_INIT_DONE_DONE <<
> > > > +		AHB_ARBITRATION_XBAR_CTRL_SMMU_INIT_DONE_SHIFT;
> > > > +	gizmo_writel(val, AHB_ARBITRATION_XBAR_CTRL);
> > > > +}
> > > > +EXPORT_SYMBOL(tegra_ahb_enable_smmu);
> > > 
> > > ok, so this is the only place where you need that global pointer. Who
> > > would call this ? Can you do runtime detection of the SoC and enable
> > > SMMU based on that ?
> > > 
> > > I mean, will this function always be called for TEGRA 3 SoCs or is there
> > > another condition to that ?
> > 
> > Only Tegra3 has SMMU.
> 
> but all of them ? In that case, you could call this from probe itself,
> right ? But an ifdef won't work in all cases, so you need to do runtime
> detection based on some revision register or cpu detection...

So far we don't have so many variants, and presently TEGRA_3x_SOC
always has a SMMU. If there were some variants of TEGRA_3x_SOC, where
some might not have SMMU, then runtime detection would make sense
there. Now it's something like TEGRA_3x_SOC == SMMU.
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