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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>
Cc: Jason Wang <jasowang@redhat.com>,
	Srivatsa Vaddagiri <svaddagi@qti.qualcomm.com>,
	Cornelia Huck <cohuck@redhat.com>,
	"virtio-dev@lists.oasis-open.org"
	<virtio-dev@lists.oasis-open.org>,
	Trilok Soni <quic_tsoni@quicinc.com>,
	Pratik Patel <quic_pratikp@quicinc.com>
Subject: Re: [virtio-dev] Re: [PATCH v1] virtio-mmio: Specify wait needed in driver during reset
Date: Mon, 16 Aug 2021 07:48:56 -0400	[thread overview]
Message-ID: <20210816074558-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20210816063550.GD5604@quicinc.com>

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
> > have:
> > 
> >         /* 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?

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