[PATCH V2 2/3] iommu: of: Ignore all errors except EPROBE_DEFER
From: laurent.pinchart@ideasonboard.com (Laurent Pinchart)
Date: 2017-05-18 10:39:19
Also in:
linux-acpi, linux-arch, linux-arm-msm, linux-devicetree, linux-iommu, linux-pci, lkml
Subsystem:
iommu subsystem, the rest · Maintainers:
Joerg Roedel, Will Deacon, Linus Torvalds
Hi Sricharan, Thank you for the patch. On Thursday 18 May 2017 15:37:09 Sricharan R wrote:
While deferring the probe of IOMMU masters, xlate and add_device callback can pass back error values like -ENODEV, which means IOMMU cannot be connected with that master for real reasons. So rather than killing the master's probe for such errors, just ignore the errors and let the master work without an IOMMU.
I don't think this is a good idea. Why should we allow IOMMU drivers to return an error if we're always going to ignore the error value ? That will lead to drivers implementing slightly different behaviours, which will be painful the day we'll need to start acting based on the error value. At the very least, if you want to give a specific meaning to -ENODEV, you should check for that value specifically and not ignore all errors other than -EPROBE_DEFER. You also need to document the meaning of the error value. This can be done in the documentation of the of_xlate operation in include/linux/iommu.h:
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 2cb54adc4a33..6ba553e7384a 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h@@ -181,7 +181,6 @@ struct iommu_resv_region { * @domain_window_disable: Disable a particular window for a domain * @domain_set_windows: Set the number of windows for a domain * @domain_get_windows: Return the number of windows for a domain - * @of_xlate: add OF master IDs to iommu grouping * @pgsize_bitmap: bitmap of all possible supported page sizes */ struct iommu_ops {
@@ -224,6 +223,11 @@ struct iommu_ops { /* Get the number of windows per domain */ u32 (*domain_get_windows)(struct iommu_domain *domain); + /** + * @of_xlate: + * + * Add OF master IDs to iommu grouping. + */ int (*of_xlate)(struct device *dev, struct of_phandle_args *args); unsigned long pgsize_bitmap;
And add documentation for the error codes there. If you want to ignore some errors returned from the add_device operation you should document it similarly, and in particular document which error check(s) need to be performed by of_xlate and which are the responsibility of add_device.
quoted hunk ↗ jump to hunk
Fixes: 7b07cbefb68d ("iommu: of: Handle IOMMU lookup failure with deferred probing or error") Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> Tested-by: Magnus Damn <redacted> Signed-off-by: Sricharan R <redacted> --- [V2] Corrected spelling/case in commit log drivers/iommu/of_iommu.c | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c index e6e9bec..f0d22c0 100644 --- a/drivers/iommu/of_iommu.c +++ b/drivers/iommu/of_iommu.c@@ -237,6 +237,12 @@ const struct iommu_ops *of_iommu_configure(structdevice *dev, ops = ERR_PTR(err); } + /* Ignore all other errors apart from EPROBE_DEFER */ + if (IS_ERR(ops) && (PTR_ERR(ops) != -EPROBE_DEFER)) { + dev_info(dev, "Adding to IOMMU failed: %ld\n", PTR_ERR(ops)); + ops = NULL; + } + return ops; }
-- Regards, Laurent Pinchart