On 2021/12/6 19:56, Joerg Roedel wrote:

On Tue, Nov 16, 2021 at 05:06:20PM +0800, Yicong Yang wrote:

quoted

Export iommu_{get,put}_resv_regions() to the modules so that the driver
can retrieve and use the reserved regions of the device.

Why should any driver bother? These functions are only used by the iommu
core to call into iommu drivers to get information about needed direct
mappings. Why drivers need this information belongs into this commit
message.

Our driver makes use of RMR[1], so we need these APIs to retrieve the reserved
memory region in the driver. The device will store the traced data to
the rmr memory and the drivers needs to know the memory address for reading
the data. Due to some hardware limitation, the device can only use direct
mapping for DMA so we need RMR when the iommu is presented and the policy
of the iommu domain is not passthrough.

[1] https://lore.kernel.org/linux-acpi/20210805080724.480-1-shameerali.kolothum.thodi@huawei.com/ (local)

Thanks,
Yicong

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