Re: [PATCH v6 10/10] xen/arm: smmuv3: Add support for SMMUv3 driver

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 25 Jan 2021, Rahul Singh wrote:
> Hello Julien,
> 
> > On 23 Jan 2021, at 11:55 am, Julien Grall <julien@xxxxxxx> wrote:
> > 
> > Hi Rahul
> > 
> > On 22/01/2021 11:37, Rahul Singh wrote:
> >> Add support for ARM architected SMMUv3 implementation. It is based on
> >> the Linux SMMUv3 driver.
> >> Driver is currently supported as Tech Preview.
> >> Major differences with regard to Linux driver are as follows:
> >> 2. Only Stage-2 translation is supported as compared to the Linux driver
> >>    that supports both Stage-1 and Stage-2 translations.
> >> 3. Use P2M  page table instead of creating one as SMMUv3 has the
> >>    capability to share the page tables with the CPU.
> >> 4. Tasklets are used in place of threaded IRQ's in Linux for event queue
> >>    and priority queue IRQ handling.
> >> 5. Latest version of the Linux SMMUv3 code implements the commands queue
> >>    access functions based on atomic operations implemented in Linux.
> >>    Atomic functions used by the commands queue access functions are not
> >>    implemented in XEN therefore we decided to port the earlier version
> >>    of the code. Atomic operations are introduced to fix the bottleneck
> >>    of the SMMU command queue insertion operation. A new algorithm for
> >>    inserting commands into the queue is introduced, which is lock-free
> >>    on the fast-path.
> >>    Consequence of reverting the patch is that the command queue
> >>    insertion will be slow for large systems as spinlock will be used to
> >>    serializes accesses from all CPUs to the single queue supported by
> >>    the hardware. Once the proper atomic operations will be available in
> >>    XEN the driver can be updated.
> >> 6. Spin lock is used in place of mutex when attaching a device to the
> >>    SMMU, as there is no blocking locks implementation available in XEN.
> >>    This might introduce latency in XEN. Need to investigate before
> >>    driver is out for tech preview.
> >> 7. PCI ATS functionality is not supported, as there is no support
> >>    available in XEN to test the functionality. Code is not tested and
> >>    compiled. Code is guarded by the flag CONFIG_PCI_ATS.
> >> 8. MSI interrupts are not supported as there is no support available in
> >>    XEN to request MSI interrupts. Code is not tested and compiled. Code
> >>    is guarded by the flag CONFIG_MSI.
> >> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> >> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> > 
> > Thank you for sending a new version. I have commited the series now.
> > 
> 
> Thank you for committing the series.

Well done, Rahul!