linux-kernel - Re: [PATCHv5 4/9] iommu/tegra: smmu: register device to iommu dynamically

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Date:	Tue, 19 Nov 2013 14:39:54 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Hiroshi Doyu <hdoyu@...dia.com>, swarren@...dia.com,
	will.deacon@....com, grant.likely@...aro.org,
	thierry.reding@...il.com, galak@...eaurora.org
CC:	mark.rutland@....com, devicetree@...r.kernel.org,
	iommu@...ts.linux-foundation.org, linux-tegra@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, lorenzo.pieralisi@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv5 4/9] iommu/tegra: smmu: register device to iommu dynamically

On 11/19/2013 02:33 AM, Hiroshi Doyu wrote:
> platform_devices are registered as IOMMU'able dynamically via
> add_device() and remove_device().
> 
> Tegra SMMU can have multiple address spaces(AS). IOMMU'able devices
> can belong to one of them. Multiple IOVA maps are created at boot-up,
> which can be attached to devices later. We reserve 2 of them for
> static assignment, AS[0] for system default, AS[1] for AHB clusters as
> protected domain from others, where there are many traditional
> pheripheral devices like USB, SD/MMC. They should be isolated from
> some smart devices like host1x for system robustness. Even if smart
> devices behaves wrongly, the traditional devices(SD/MMC, USB) wouldn't
> be affected, and the system could continue most likely. DMA API(ARM)
> needs ARM_DMA_USE_IOMMU to be enabled.

> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c

> +static int smmu_iommu_add_device(struct device *dev)
> +{
> +	int err = -EPROBE_DEFER;
> +	u32 swgroups = dev->platform_data;
> +	struct dma_iommu_mapping *map = NULL;
> +
> +	if (test_bit(TEGRA_SWGROUP_PPCS, swgroups))
> +		map = smmu_handle->map[SYSTEM_PROTECTED];
> +	else
> +		map = smmu_handle->map[SYSTEM_DEFAULT];
> +
> +	if (map)
> +		err = arm_iommu_attach_device(dev, map);
> +	else
> +		return -EPROBE_DEFER;

Given that patch 2 exists, if this test fails, then surely the
appropriate error code is some fatal error, not -EPROBE_DEFER; any
deferrals should have happened long before this point.
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