Hi Joerg,

From: Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 1/2] ARM: IOMMU: Tegra20: Add iommu_ops for GART driver
Date: Mon, 23 Jan 2012 16:00:48 +0100
Message-ID: [ref]

Hi,

first, some questions about the GART on your platform.

1) How many GARTs are usually implemented? One GART per device or is
   there a single GART covering all devices, or a mix of both?

There's a single GART in the system which takes care of all devices.

2) Are devices allowed to DMA outside of the remappable range or will
   this fail?

Fail.

Besides that I think IOMMU-API is not yet fully ready for GART-like
drivers like this one. But I will merge it anyway to get things moving.
But please answer or fix my objections first.

On Thu, Jan 05, 2012 at 09:11:48AM +0200, Hiroshi DOYU wrote:

quoted

+static void gart_iommu_domain_destroy(struct iommu_domain *domain)
+{
+	struct gart_device *gart = domain->priv;
+
+	spin_lock(&gart->client_lock);
+	if (!list_empty(&gart->client)) {
+		struct gart_client *c;
+
+		list_for_each_entry(c, &gart->client, list)
+			dev_err(gart->dev,
+				"%s is still attached\n", dev_name(c->dev));
+	}
+	spin_unlock(&gart->client_lock);

gart needs a NULL check. When you create a domain and immediatly destroy
it without ever attaching a device this code will dereference a NULL
pointer.

Fixed.

As a general improvement I suggest that you introduce a gart_domain
structure and store it in domain->priv (assigned in domain_init) instead
of using the hardware descriptor.

quoted

+static int gart_iommu_attach_dev(struct iommu_domain *domain,
+				 struct device *dev)
+{
+	struct gart_device *gart;
+	struct gart_client *client, *c;
+	int err = 0;
+
+	gart = dev_get_drvdata(dev->parent);
+	if (!gart)
+		return -EINVAL;
+	domain->priv = gart;

What happens when devices behind different GARTs are assigned to the
same domain? domain->priv can only hold a pointer to one hardware GART.
This can be solved by a 'struct gart_domain' holding a linked list to
all gart_devices in this domain.

As discussed in SMMU thread, I'll revisit the above multiple iommu
device support later.

Attached the update patch.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-ARM-IOMMU-Tegra20-Add-iommu_ops-for-GART-driver.patch
Type: text/x-patch
Size: 14203 bytes
Desc: 0001-ARM-IOMMU-Tegra20-Add-iommu_ops-for-GART-driver.patch
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20120125/763fd94b/attachment.bin>