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Subject: Re: [PATCH v2 01/11] xen/manage: keep track of the on-going suspend
 mode
To:     Anchal Agarwal <anchalag@amazon.com>
Cc:     Stefano Stabellini <sstabellini@kernel.org>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
        jgross@suse.com, linux-pm@vger.kernel.org, linux-mm@kvack.org,
        kamatam@amazon.com, konrad.wilk@oracle.com, roger.pau@citrix.com,
        axboe@kernel.dk, davem@davemloft.net, rjw@rjwysocki.net,
        len.brown@intel.com, pavel@ucw.cz, peterz@infradead.org,
        eduval@amazon.com, sblbir@amazon.com,
        xen-devel@lists.xenproject.org, vkuznets@redhat.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        dwmw@amazon.co.uk, benh@kernel.crashing.org
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From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Fri, 31 Jul 2020 10:13:48 -0400
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On 7/30/20 7:06 PM, Anchal Agarwal wrote:
> On Mon, Jul 27, 2020 at 06:08:29PM -0400, Boris Ostrovsky wrote:
>> CAUTION: This email originated from outside of the organization. Do no=
t click links or open attachments unless you can confirm the sender and k=
now the content is safe.
>>
>>
>>
>> On 7/24/20 7:01 PM, Stefano Stabellini wrote:
>>> Yes, it does, thank you. I'd rather not introduce unknown regressions=
 so
>>> I would recommend to add an arch-specific check on registering
>>> freeze/thaw/restore handlers. Maybe something like the following:
>>>
>>> #ifdef CONFIG_X86
>>>     .freeze =3D blkfront_freeze,
>>>     .thaw =3D blkfront_restore,
>>>     .restore =3D blkfront_restore
>>> #endif
>>>
>>>
>>> maybe Boris has a better suggestion on how to do it
>>
>> An alternative might be to still install pm notifier in
>> drivers/xen/manage.c (I think as result of latest discussions we decid=
ed
>> we won't need it) and return -ENOTSUPP for ARM for
>> PM_HIBERNATION_PREPARE and friends. Would that work?
>>
> I think the question here is for registering driver specific freeze/tha=
w/restore
> callbacks for x86 only. I have dropped the pm_notifier in the v3 still =
pending
> testing. So I think just registering driver specific callbacks for x86 =
only is a
> good option. What do you think?


I suggested using the notifier under assumption that if it returns an
error then that will prevent callbacks to be called because hibernation
will be effectively disabled. But I haven't looked at PM code so I don't
know whether this is actually the case.


The advantage of doing it in the notifier is that instead of adding
ifdefs to each driver you will be able to prevent callbacks from a
single place. Plus you can use this do disable hibernation for PVH dom0
as well.


-boris