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SubjectRe: [PATCHv3 3/4] iommu/tegra: smmu: Refrain from accessing to AHB
From: Stephen Warren <swarren@wwwdotorg.org>
Subject: Re: [PATCHv3 3/4] iommu/tegra: smmu: Refrain from accessing to AHB
Date: Thu, 3 May 2012 19:48:25 +0200
Message-ID: <4FA2C4E9.2080509@wwwdotorg.org>

> On 05/03/2012 10:05 AM, Hiroshi DOYU wrote:
> > Use "tegra_ahb_enable_smmu()" to inform AHB that SMMU is
> > ready, instead of directly aceessing AHB registers.
>
> You need to make the Kconfig option for the SMMU either depend on or
> select the TEGRA_AHB option. If you don't, then if someone disables the
> AHB driver, the SMMU driver may still build, yet fail to link since the
> AHB API it calls doesn't exist.
>
> > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
>
> > @@ -398,10 +388,8 @@ static void smmu_setup_regs(struct smmu_device *smmu)
> >
> > smmu_flush_regs(smmu, 1);
> >
> > - val = ahb_read(smmu, AHB_XBAR_CTRL);
> > - val |= AHB_XBAR_CTRL_SMMU_INIT_DONE_DONE <<
> > - AHB_XBAR_CTRL_SMMU_INIT_DONE_SHIFT;
> > - ahb_write(smmu, val, AHB_XBAR_CTRL);
> > + err = tegra_ahb_enable_smmu(smmu->ahb);
> > + return err;
>
> You can just "return tegra_ahb_..." here.
>
> > @@ -911,14 +899,16 @@ static int tegra_smmu_probe(struct platform_device *pdev)
>
> > + smmu->ahb = of_parse_phandle(pdev->dev.of_node, "ahb", 0);
>
> Hmm, "ahb" should probably be "nvidia,ahb".

Does this mean the following in dts?

ahb: ahb@6000c004 {
compatible = "nvidia,tegra30-ahb";
reg = <0x6000c004 0x14c>; /* AHB Arbitration + Gizmo Controller */
};
smmu: smmu@7000f000 {
nvidia,ahb = &ahb;
}; ^^^^^^^^^^

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