Re: [PATCH v4 2/6] ACPI: Move IOMMU setup code out of IORT

On 2021-06-18 08:41, Jean-Philippe Brucker wrote:

Hi Eric,

On Wed, Jun 16, 2021 at 11:35:13AM +0200, Eric Auger wrote:

quoted

quoted

-const struct iommu_ops *iort_iommu_configure_id(struct device *dev,
-						const u32 *id_in)
+int iort_iommu_configure_id(struct device *dev, const u32 *id_in)
  {
  	struct acpi_iort_node *node;
-	const struct iommu_ops *ops;
+	const struct iommu_ops *ops = NULL;

Oops, I need to remove this (and add -Werror to my tests.)

quoted

quoted

+static const struct iommu_ops *acpi_iommu_configure_id(struct device *dev,
+						       const u32 *id_in)
+{
+	int err;
+	const struct iommu_ops *ops;
+
+	/*
+	 * If we already translated the fwspec there is nothing left to do,
+	 * return the iommu_ops.
+	 */
+	ops = acpi_iommu_fwspec_ops(dev);
+	if (ops)
+		return ops;
+
+	err = iort_iommu_configure_id(dev, id_in);
+
+	/*
+	 * If we have reason to believe the IOMMU driver missed the initial
+	 * add_device callback for dev, replay it to get things in order.
+	 */
+	if (!err && dev->bus && !device_iommu_mapped(dev))
+		err = iommu_probe_device(dev);

Previously we had:
     if (!err) {
         ops = iort_fwspec_iommu_ops(dev);
         err = iort_add_device_replay(dev);
     }

Please can you explain the transform? I see the

acpi_iommu_fwspec_ops call below but is it not straightforward to me.

I figured that iort_add_device_replay() is only used once and is
sufficiently simple to be inlined manually (saving 10 lines). Then I
replaced the ops assignment with returns, which saves another line and may
be slightly clearer?  I guess it's mostly a matter of taste, the behavior
should be exactly the same.

Right, IIRC the multiple assignments to ops were more of a haphazard 
evolution inherited from the DT version, and looking at it now I think 
the multiple-return is indeed a bit nicer.

Similarly, it looks like the factoring out of iort_add_device_replay() 
was originally an attempt to encapsulate the IOMMU_API dependency, but 
things have moved around a lot since then, so that seems like a sensible 
simplification to make too.

Robin.

quoted

Also the comment mentions replay. Unsure if it is still OK.

The "replay" part is, but "add_device" isn't accurate because it has since
been replaced by probe_device. I'll refresh the comment.

Thanks,
Jean
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