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Re: [PATCH v6 10/10] xen/arm: smmuv3: Add support for SMMUv3 driver
- To: Rahul Singh <rahul.singh@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Julien Grall <julien@xxxxxxx>
- Date: Sat, 23 Jan 2021 11:55:07 +0000
- Cc: bertrand.marquis@xxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Sat, 23 Jan 2021 11:55:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Cheers,
--
Julien Grall
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