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Subject: Re: [PATCH v1] virtio-mmio: Specify wait needed in driver during reset
On Mon, Jul 26, 2021 at 02:17:08PM +0000, Srivatsa Vaddagiri wrote: > > On Mon, Jul 26, 2021 at 01:36:56PM +0200, Cornelia Huck wrote: > > > On Mon, Jul 26 2021, Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com> wrote: > > > > > > >> > +indicated by a read of \field{Status} returning 0. Such a device MUST > also > > > >> > fail to accept > > > >> > +FEATURES_OK bit if driver does not negotiate > VIRTIO_F_MMIO_RESET_WAIT. > > > >> > > > >> So, this basically means that an older driver that does not know the new > > > >> feature bit will not work with devices offering this bit, even if it did > > > >> poll? This seems acceptable, I just wanted to spell it out. > > > > > > > > Yes I believe that's the desired result. Device has no way to know if > driver > > > > will poll for reset completion or not unless it accepts the feature. > > > > Are you suggesting we explicitly put in some text in spec to that > > > > effect? > > > > > > Not sure whether it is needed (do others have an opinion?), but probably > > > not. > > > > What about resets before FEATURES_OK? How are these handled? > > From device perspective, it's reset logic will always be same, independent of > when reset was performed by driver (before or after feature negotiation). A > driver that does not wait for reset completion will see undefined behavior > after > reset until it discovers that feature negotiation has failed? > > - vatsa Hmm. that doesn't sound too good. Makes using feature negotiation for this kind of useless ... Device can actually detect a read from status, right? Maybe if it sees status was not read it can just stay in reset state and not exit it? > --- > > 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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