Hi Laurent,
On 5/18/2017 4:09 PM, Laurent Pinchart wrote:
> 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.
>
The of_iommu_configure interface, before this series, was returning either
correct 'iommu_ops' or NULL. Also there was no return value from
of_dma_configure which calls of_iommu_configure. This means that if we block
only -ENODEV now and let the other errors, the probe of the master devices
can be killed for reasons apart from deferring. This would be a change in
behavior introduced. All of xlate, add_device, of_pci_map_rid and others
can return values apart from -ENODEV. So was thinking that restoring the
old behavior, except for returning EPROBE_DEFER was the better thing to do ?
Regards,
Sricharan
> 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.
>
>> Fixes: 7b07cbefb68d ("iommu: of: Handle IOMMU lookup failure with deferred
>> probing or error")
>> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
>> Tested-by: Magnus Damn <magnus.damn@xxxxxxxxx>
>> Signed-off-by: Sricharan R <sricharan@xxxxxxxxxxxxxx>
>> ---
>> [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(struct
>> device *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;
>> }
>
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