linux-kernel - Re: [PATCHv3 2/4] ARM: tegra: Add SMMU enabler in AHB

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Message-ID: <20120426083716.69efa6f5b58200e265b2e867@nvidia.com>
Date:	Thu, 26 Apr 2012 08:37:16 +0300
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"balbi@...com" <balbi@...com>,
	Stephen Warren <swarren@...dotorg.org>
CC:	Stephen Warren <swarren@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Colin Cross <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	Russell King <linux@....linux.org.uk>,
	"Tony Lindgren" <tony@...mide.com>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	Jamie Iles <jamie@...ieiles.com>,
	"Rob Herring" <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 2/4] ARM: tegra: Add SMMU enabler in AHB

On Wed, 25 Apr 2012 17:51:50 +0200
Stephen Warren <swarren@...dotorg.org> wrote:

> On 04/25/2012 05:29 AM, Felipe Balbi wrote:
> > Hi,
> > 
> > On Wed, Apr 25, 2012 at 02:07:37PM +0300, Hiroshi DOYU wrote:
> >> Add extern func, "tegra_ahb_enable_smmu()" to inform AHB that SMMU is
> >> ready.
> 
> >> +#ifdef CONFIG_ARCH_TEGRA_3x_SOC
> >> +static int __tegra_ahb_enable_smmu(struct device *dev, void *data)
> >> +{
> >> +	u32 val;
> >> +	struct tegra_ahb *ahb = dev_get_drvdata(dev);
> >> +
> >> +	val = gizmo_readl(ahb, AHB_ARBITRATION_XBAR_CTRL);
> >> +	val |= AHB_ARBITRATION_XBAR_CTRL_SMMU_INIT_DONE;
> >> +	gizmo_writel(ahb, val, AHB_ARBITRATION_XBAR_CTRL);
> >> +	return 0;
> >> +}
> >> +
> >> +int tegra_ahb_enable_smmu(void)
> >> +{
> >> +	return driver_for_each_device(&tegra_ahb_driver.driver, NULL, NULL,
> >> +				      __tegra_ahb_enable_smmu);
> >> +}
> >> +EXPORT_SYMBOL(tegra_ahb_enable_smmu);
> >> +#endif
> > 
> > this is still not correct. If you will always call this whenever you run
> > on tegra 3, why do you even expose this function ?
> 
> I think the issue is that this function should only be called after the
> SMMU driver has initialized the SMMU, and it's ready to be activated.

Right. "tegra_ahb_enable_smmu()" is not supposed to be called at
tegra_ahb_probe(), but it is always expected to be called after SMMU
is initialized/gets ready.

The sequence is:
 1, AHB is probed.
 ...<any other operations>...
 2, SMMU is probed.
 ...<any other operations>...
 3, SMMU is ready, then,
 4, SMMU lets AHB know that SMMU is ready to be used by AHB clients.

The above step 4 is "tegra_ahb_enable_smmu()".
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