On Jun 9 16:52, John Levon wrote: > On Thu, Jun 09, 2022 at 08:29:30AM -0600, Keith Busch wrote: > > > On Wed, Jun 08, 2022 at 10:55:30PM +0200, Klaus Jensen wrote: > > > > > > Keith, is this a bug in the kernel? If the code here would expect the > > > doorbell buffer to be updated for the admin queue as well, would we > > > break? > > > > The admin queue has to be created before db buffer can be set up, so we > > can't > > rely on it. And this is a performance feature. Admin commands have never > > been > > considered performant, so we decided not to consider it though the spec > > allows > > it.
It's not really a question of whether or not the spec *allows* it. If our device chooses to be compliant here, then it will read invalid doorbell values if drivers doesnt update the admin doorbell buffer. > > It's not just unnecessary, but enabling shadow doorbells on admin queues will > actively break device implementations (such as SPDK), which have had to > presume > that driver implementations don't use shadow doorbells for the admin queue. > I'm ok with following the concensus here, but we all agree that this is a blatant spec violation that ended up manifesting itself down the stack, right? So... if QEMU wants to be compliant here, I guess we could ask the kernel to introduce a quirk for *compliant* controllers. Now, THAT would be a first! Not sure if I am being serious or not here ;)
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