linux-kernel - Re: [PATCH 2/3] iommu/tegra: smmu: Add device tree support for SMMU

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Message-ID: <4F959F10.9010908@wwwdotorg.org>
Date:	Mon, 23 Apr 2012 12:27:28 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Hiroshi DOYU <hdoyu@...dia.com>
CC:	linux-tegra@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Joerg Roedel <joerg.roedel@....com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] iommu/tegra: smmu: Add device tree support for SMMU

On 04/23/2012 05:58 AM, Hiroshi DOYU wrote:
> Add device tree support for Tegra30 IOMMU(SMMU).

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

> +	err = of_parse_dma_window(dev->of_node, "dma-window", 0, NULL,
> +				  &base, &size);

This patch also depends on "dt: Add general DMA window parser" that you
sent earlier.

> +	asids = be32_to_cpup(of_get_property(dev->of_node, "asids", NULL));
> +	if (!asids)
> +		return -ENODEV;

What if of_get_property() fails?

BTW, does the # ASIDs vary? I wonder if it's worth representing it in
the device tree or not. If this driver has a chance of working
unmodified on some future chip just by updating this DT property without
any code changes, then it seems reasonable to have it in DT.
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