From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>
Subject: Re: [PATCHv7 02/12] iommu/of: introduce a global iommu device list
Date: Mon, 16 Dec 2013 11:32:47 -0700
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To: Hiroshi Doyu <hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>, swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, robherring2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org
Cc: mark.rutland-5wv7dgnIgG8@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lorenzo.pieralisi-5wv7dgnIgG8@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
List-Id: devicetree@vger.kernel.org

On 12/12/2013 12:57 AM, Hiroshi Doyu wrote:
> This enables to find an populated IOMMU device via a device node. This
> can be used to see if an dependee IOMMU is populated or not to keep
> correct device population order. Client devices need to wait an IOMMU
> to be populated.
> 
> Suggested by Thierry Reding and copied his example code.

> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c

> +static struct iommu *of_find_iommu_by_node(struct device_node *np)
> +{
> +	struct iommu *iommu;
> +
> +	mutex_lock(&iommus_lock);
> +	list_for_each_entry(iommu, &iommus_list, list) {
> +		if (iommu->dev->of_node == np) {
> +			mutex_unlock(&iommus_lock);

Now that the list is unlocked, the IOMMU could be removed from the list,
and the driver unregistered. Should you do something like
iommu_get(iommu); before the mutex_unlock() call, and call iommu_put()
somewhere (i.e. in the next patch ...)?