linux-kernel - Re: [PATCH 3/4] iommu/exynos: Add iommu driver for Exynos4 Platforms

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Date:	Mon, 26 Sep 2011 10:59:16 +0300
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	pullip.cho@...sung.com
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joerg.roedel@....com" <joerg.roedel@....com>,
	이상현 <sanghyun75.lee@...sung.com>,
	김국진 <kgene.kim@...sung.com>,
	김영락 <younglak1004.kim@...sung.com>
Subject: Re: [PATCH 3/4] iommu/exynos: Add iommu driver for Exynos4 Platforms

2011/9/24 조경호 <pullip.cho@...sung.com>:
> This is the System MMU driver and IOMMU API implementation for
> Exynos4 SOC platforms. Exynos4 platforms has more than 10 System
> MMUs dedicated for each multimedia accellerators.
>
> Signed-off-by: KyongHo Cho <pullip.cho@...sung.com>
...
> +static int exynos_iommu_fault_handler(struct iommu_domain *domain,
> +                       struct device *dev, unsigned long iova, int flags)
> +{
> +       struct exynos_iommu_domain *priv = domain->priv;
> +
> +       dev_err(priv->dev, "%s occured at %p(Page table base: %p)\n",
> +                               sysmmu_fault_name[flags], (void *)iova,
> +                               (void *)(__pa(priv->pgtable)));
> +       dev_err(priv->dev, "\t\tGenerating Kernel OOPS...\n");
> +       dev_err(priv->dev, "\t\tbecause it is unrecoverable.\n");
> +       dev_err(priv->dev,
> +               "\t\tSet Fault handler with iommu_set_fault_handler().\n");
> +       dev_err(priv->dev, "\t\tto handle System MMU fault.\n");
> +
> +       BUG();
> +
> +       return 0;
> +}
> +
> +static int exynos_iommu_domain_init(struct iommu_domain *domain)
> +{
...
> +       iommu_set_fault_handler(domain, &exynos_iommu_fault_handler);

It doesn't make a lot of sense to set an iommu fault handler here; the
intention of iommu_set_fault_handler() is to allow upper layers to do
that.

Moreover, exynos_sysmmu_irq() anyway knows whenever a fault occurs, so
calling report_iommu_fault() just to have it call into the driver
again seems redundant.

If you want an exynos-specific behavior to occur whenever there's an
iommu fault, you should do that in exynos_sysmmu_irq itself. If you
just want a generic default logging behavior to occur whenever there's
no other fault handler installed, you might even want to consider
adding it to the IOMMU core.
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