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Subject: Re: [virtio-dev] Re: [PATCH v1] virtio-mmio: Specify wait needed in driver during reset

在 2021/8/16 下午7:48, Michael S. Tsirkin 写道:
On Mon, Aug 16, 2021 at 12:05:50PM +0530, Srivatsa Vaddagiri wrote:
* Michael S. Tsirkin <mst@redhat.com> [2021-08-16 01:35:46]:

So thinking about all this, quite early in the setup process we

         /* Figure out what features the device supports. */
         device_features = dev->config->get_features(dev);

isn't this sufficient? this will flush out
all writes and device can defer responding to reads
until reset is complete.
Hmm not sure if that's possible in all MMIO devices? I think a while back Jason
felt some of the MMIO devices, their registers could act as plain DRAM for
reads, which means device can't block such reads?

- vatsa
Is it worth bothering about theoretical issues though? Jason what is
your take?

Re-read the spec, and it said


MMIO Device Register Layout


I believe plain DRAM will not behave like a register. So we don't need to worry about that.

But they are indeed devices that act as a plain DRAM for their control path, which might requires new transports[1].

Another question is that what makes PCI differ from MMIO. (E.g PCI requires a re-read but MMIO doesn't)

[1] https://lkml.org/lkml/2020/9/1/255


Qualcomm Innovation Center, Inc. is submitting the attached "feedback" as a
non-member to the virtio-dev mailing list for consideration and inclusion.

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