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

["Edgar E. Iglesias" <edgar.iglesias@xilinx.com>]

On Wed, Jan 24, 2018 at 07:04:35PM +0100, Mirela Simonovic wrote:
> 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.

Having said that it may still be useful from a patch review perspective
to incrementally add things. Perhaps the IOMMU suspending support could
come in follow-up patch series if others agree.

Best regards,
Edgar



> >
> >
> >>In other words, each involved platform device driver in Xen on ARM
> >>(IOMMU-XX, UART-XX, etc) should have suspend/resume callbacks
> >>implemented.
> 
> 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
> 2. IOMMU
> 3. UART
> 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!
> 
> Cheers,
> Mirela
> >Yes agreed.
> >
> >Best regards,
> >Edgar
> >
> >
> >>-- 
> >>Regards,
> >>
> >>Oleksandr Tyshchenko
> 

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