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

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Message-ID: <20120427.094826.1181797260264746303.hdoyu@nvidia.com>
Date:	Fri, 27 Apr 2012 08:48:26 +0200
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"balbi@...com" <balbi@...com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	Stephen Warren <swarren@...dia.com>
CC:	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"ccross@...roid.com" <ccross@...roid.com>,
	"olof@...om.net" <olof@...om.net>,
	"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-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv3 2/4] ARM: tegra: Add SMMU enabler in AHB

From: Felipe Balbi <balbi@...com>
Subject: Re: [PATCHv3 2/4] ARM: tegra: Add SMMU enabler in AHB
Date: Thu, 26 Apr 2012 22:38:48 +0200
Message-ID: <20120426203847.GC30690@...en.pp.htv.fi>

> * PGP Signed by an unknown key
> 
> Hi,
> 
> On Thu, Apr 26, 2012 at 02:32:56PM -0600, Stephen Warren wrote:
> > On 04/26/2012 02:26 PM, Felipe Balbi wrote:
> > > Hi,
> > > 
> > > On Thu, Apr 26, 2012 at 01:55:13PM -0600, Stephen Warren wrote:
> > >> On 04/25/2012 05:07 AM, 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)
> > >> ...
> > >>> +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
> > >>
> > >> That looks like a neat solution to avoid having a global device object.
> > > 
> > > except that it won't work always. If you happen to have two AHB bridges,
> > > each using a separate smmu but only one smmu is ready, this will set
> > > SMMU_INIT_DONE on both bridges.
> > 
> > There is only 1.
> 
> that's why there's a "if you happen to have" statement. If you stick to
> this "there is only 1" argument, why do you even make this into a
> platform driver ? Just stick the entire code hidden on the
> machine_init() code. Drivers a supposed to be able to instantiated
> multiple times and always work, this method won't work if tegra99999
> ends up with two AHB bridges/SMMUs
> 
> > >> However, if that driver_for_each_device finds no devices, the function
> > >> still succeeds. That doesn't seem right, and doesn't allow e.g. the SMMU
> > >> to defer its probe until the AHB driver has completed.
> > >>
> > >> Perhaps add a local int variable to tegra_ahb_enable_smmu(), pass the
> > >> address to __tegra_ahb_enable_smmu, and have it increment the int. Then,
> > >> after calling driver_for_each_device,:
> > >>
> > >> if (!ahb_device_count)
> > >>     return -EPROBE_DEFER
> > >> if (WARN_ON(ahb_device_count != 1))
> > >>     return -EINVAL;
> > >> return 0;
> > > 
> > > that would look, well, weird. Why don't you just different initcall
> > > leves for this ? Maybe smmu goes into postcore_initcall() and tegra_ahb
> > > goes into postcore_initcall_sync() ?? then you know that SMMU will be
> > > ready by the time you call tegra_ahb probe. Well, unless smmu's probe
> > > fail, but then again, IIUC it won't work anyway...
> > 
> > Uggh. I'd rather all these devices just got instantiated from device
> > tree and relied on deferred probe to manage any ordering, rather than
> > playing complex games with multiple initcall levels (and in the end
> > probably having to invent more and more initcall levels to correctly
> > represent all the dependencies).
> 
> then do that... it'll be better than current trickery with
> driver_for_each_device() and my initcall trickery ;-)

Then, what about something like the following?

 static int tegra_ahb_match_by_smmu(struct device *dev, void *data)
 {
 	struct tegra_ahb *ahb = dev_get_drvdata(dev);
 	struct device_node *dn = data;
 
 	return (ahb->dev->of_node == dn) ? 1 : 0
 }
 
 int tegra_ahb_enable_smmu(struct device_node *ahb)
 {
 	struct device *dev;
 	u32 val;
 
 	dev = driver_find_device(&tegra_ahb_driver.driver, NULL, ahb,
 				 tegra_ahb_match_by_smmu);
 	if (!dev)
 		return -ENODEV;
 
 	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;
 }
 EXPORT_SYMBOL(tegra_ahb_enable_smmu);

	Modified arch/arm/boot/dts/tegra30.dtsi
diff --git a/arch/arm/boot/dts/tegra30.dtsi b/arch/arm/boot/dts/tegra30.dtsi
index 655bc47..28f9138 100644
--- a/arch/arm/boot/dts/tegra30.dtsi
+++ b/arch/arm/boot/dts/tegra30.dtsi
@@ -242,5 +242,6 @@
 	smmu {
 		compatible = "nvidia,tegra30-smmu";
 		mc = <&mc>;
+		ahb = <&ahb>;
 	};
 };
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