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Re: [Xen-devel] [RFC v2] xen/arm: Suspend to RAM Support in Xen for ARM

Hi Oleksandr, Edgar,

Thanks, you're right.

On 01/23/2018 12:58 PM, Edgar E. Iglesias wrote:
On Tue, Jan 23, 2018 at 01:52:50PM +0200, Oleksandr Tyshchenko wrote:
Hi Mirela,

Just some remarks regarding the scope of work:

+In addition, the following have to be implemented:
+* Suspend/resume vCPU (triggered by vSYSTEM_SUSPEND call)
+* Suspend/resume Xen (triggered by vSYSTEM_SUSPEND called by Dom0), including:
+       * Disable wathdog on suspend, enable it on resume
+       * Pause domains on suspend, unpause them on resume
+       * Disable non-boot pCPUs on suspend, enable them on resume
+       * Save/restore of GIC configuration
+       * Suspend/resume timer
+       * Save/restore of EL2 context
+       * Implement resume entry point in Xen, including MMU configuration

I think that saving/restoring IOMMU registers/context should be
implemented as well.
Yes, good point.
Mirela, I think that in the ZU+ case the IOMMU actually gets powered down
with the FPD.

Yes, it is in FPD.

In other words, each involved platform device driver in Xen on ARM
(IOMMU-XX, UART-XX, etc) should have suspend/resume callbacks

Yes, callback should be platform specific but not each platform has to have all callbacks implemented. E.g. on ZU+ UART is in differrent power domain compared to APU/Xen. Xen can suspend and its power domain can go down even if UART is not suspended. However, suspending UART even in this case may be beneficial from power perspective. We should definitely provide the option to implement the callback.

AFAIU, the following devices has to be suspended:
1. timer
4. GIC

Please let me know if I missed something. I'll update this in next design spec version. Thank you very much for good feedback!

Yes agreed.

Best regards,


Oleksandr Tyshchenko

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