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Subject: Re: [virtio-dev] Re: [PATCH v1] virtio-mmio: Specify wait needed in driver during reset
On Wed, Aug 18, 2021 at 1:15 PM Srivatsa Vaddagiri <quic_svaddagi@quicinc.com> wrote: > > * Jason Wang <jasowang@redhat.com> [2021-08-18 10:54:37]: > > > >I think the option we discussed earlier of a new feature bit seems less > > >intrusive than incrementing MMIO version? > > > > > >https://lists.oasis-open.org/archives/virtio-dev/202107/msg00168.html > > > > > > Using features will result some interesting question: > > > > 1) the drivers usually reset the device before feature negotiation > > 2) it means the driver must mandate this behavior even before feature > > negotiation is done > > > > We don't have those issue if we increase the version (but it looks more > > intrusive). > > Hmm ..are you suggesting that we read the Version register as part of reset code > and do the wait part only for v3 device? We only need to read the version once (see virtio_mmio_probe()). So it could be something like if (vm_dev->version == 0x3) { while (readl(vm_dev->base + VIRTIO_MMIO_STATUS)) msleep(1); } > Otherwise we have the same issue as > feature bit with version change also. > > Can't the driver do the same with feature register also? Do poll if > WAIT_FOR_RESET_COMPLETION feature bit is set, which can happen before feature > negotiation is complete. The possible issue is that the feature negotiation is not done at that time. Thanks > > - vatsa > > -- > 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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