Re: [PATCH 05/23] cxl/pci: Don't poll doorbell for mailbox access

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On 21-11-29 11:37:34, Dan Williams wrote:
> On Mon, Nov 29, 2021 at 11:32 AM Ben Widawsky <ben.widawsky@xxxxxxxxx> wrote:
> [..]
> > >
> > > Right, there's no harm in the check, it just seems overly paranoid to
> > > me if it was already checked once. Until a doorbell timeout happens
> > > it's an extra MMIO cycle that can saved for a "what happened?" check
> > > after a timeout.
> >
> > Well I suspect we're just rearranging the deck chairs on the Titanic now, but...
> 
> Not so much, just trying to get this driver in line with other error
> handling designs.

Okay. I shall remove it then.

> 
> > I see doorbell timeouts as disconnected from whether or not the mailbox
> > interface is ready. If they were the same, we wouldn't need both bits and we
> > could just wait extra long for the doorbell when probing.
> >
> > In other words, I expect if the interface goes unready, doorbell timeout will
> > occur, but I don't think we should assume if doorbell timeout occurs, the
> > interface is no longer ready. I don't purport to know why a doorbell timeout
> > might occur while the interface remains available (likely a firmware bug, I
> > presume).
> >
> > It does seem interesting to check if the interface is no longer ready on timeout
> > though.
> 
> So I'm just modeling this off of NVME error handling where there is a
> Controller Fatal Status bit that could be checked every transaction,
> but instead the driver waits until a command timeout to collect if the
> device went fatal / not-ready.

No error interrupts?



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