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Tsirkin" To: Parav Pandit Cc: Zhu Lingshan , "cohuck@redhat.com" , "jasowang@redhat.com" , "virtio-comment@lists.linux.dev" , Eugenio =?iso-8859-1?Q?P=E9rez?= , David Stevens Subject: Re: [PATCH V7 v7] virtio: introduce SUSPEND bit in device status Message-ID: <20240813040219-mutt-send-email-mst@kernel.org> References: <20240801113516.22155-1-lingshan.zhu@amd.com> <20240813033547-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtio-comment@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Aug 13, 2024 at 07:58:32AM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin > > Sent: Tuesday, August 13, 2024 1:22 PM > > > Removing intel email id again to avoid constant bouncing messages. Thanks. > > On Tue, Aug 13, 2024 at 04:42:06AM +0000, Parav Pandit wrote: > > > a. suspending a device is non frequent operation (in order of N > > operations/sec, where N is roughly in range of 10 or 100) per device? > > > b. A software-based device may not always want to force VM_EXIT on read > > and write on the device_status register? > > > > I just see where this is going. Parav, if you want a device with as little as > > possible memory on it, using DMA as much as possible, what you want is > > develop an alternative transport that will let you control status without using > > memory accesses. > No, there is no need of DMA here. > This is not about less memory either. OK, sorry. I misunderstood. > As I explained, the challenge is implementing suspend bits to operate at sub-microsecond level granularity. Yes, I think the proposal is too vague on how all this happens. Replied separately. > > This will also, with time, allow doing this for existing config space. > > We aren't blocking all spec development until you do, and the tradeoff of > > easy to debug, robust MMIO control versus complex but maybe cheaper for > > some hardware vendors DMA based access is up to the device. > > > No one is blocking the spec etc. Not sure why you say that. > The idea is to have suspend as command register, and its status to reflect in the existing device_status. > > Last time you recommended to only make design suggestion and not go down the exact details of the bit and let author to fix it. > > If you prefer to discuss the bit level details, it looks good to me to go to that details. Sorry, reacted too early. > > -- > > MST