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From:   Jassi Brar <jassisinghbrar@gmail.com>
Date:   Thu, 16 Feb 2023 22:04:17 -0600
Message-ID: <CABb+yY2u0LNiwiJeOwhYU69U_m+5bx5rsHOk5jbyJTRbVcjeYw@mail.gmail.com>
Subject: Re: [PATCH v1 0/7] MPFS system controller/mailbox fixes
To:     Conor Dooley <conor@kernel.org>
Cc:     Conor Dooley <conor.dooley@microchip.com>,
        Daire McNamara <daire.mcnamara@microchip.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
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On Thu, Feb 16, 2023 at 4:24 PM Conor Dooley <conor@kernel.org> wrote:
> >
> > > > Secondly, I have a question about what to do if a service does fail, but
> > > > not due to a timeout - eg the above example where the "new" image for
> > > > the FPGA is actually older than the one that currently exists.
> > > > Ideally, if a service fails due to something other than the transaction
> > > > timing out, I would go and read the status registers to see what the
> > > > cause of failure was.
> > > > I could not find a function in the mailbox framework that allows the
> > > > client to request that sort of information from the client. Trying to
> > > > do something with the auxiliary bus, or exporting some function to a
> > > > device specific header seemed like a circumvention of the mailbox
> > > > framework.
> > > > Do you think it would be a good idea to implement something like
> > > > mbox_client_peek_status(struct mbox_chan *chan, void *data) to allow
> > > > clients to request this type of information?
> > > >
> > > .last_tx_done() is supposed to make sure everything is ok.
> >
> > Hm, might've explained badly as I think you've misunderstood. Or (see
> > below) I might have mistakenly thought that last_tx_done() was only meant
> > to signify that tx was done.
> >
> > Anyways, I'll try to clarify.
> > Some services don't set a status, but whether a status is, or isn't,
> > set has nothing to do with whether the service has completed.
> > One service that sets a status is "Authenticate Bitstream". This
> > service sets a status of 0x0 if the bitstream in question is okay _and_
> > something that the FPGA can be upgraded to. It returns a failure of 0x18
> > if the bitstream is valid _but_ is the same as that currently programmed.
> > (and of course a whole host of other possible errors in-between)
> >
> > These statuses, and whether they are a bad outcome or not, is dependant
> > on the service and I don't think should be handled in the mailbox
> > controller driver.
> >
> > > If the expected status bit is "sometimes not set", that means that bit
> > > is not the complete status.
> >
> > If the "busy" bit goes low, then the transmission must be complete,
> > there should be no need to check other bits for *completion*, but...
> >
> > > You have to check multiple registers to
> > > detect if and what caused the failure.
> >
> > ...maybe I have just misunderstood the role of .last_tx_done(). The
> > comment in mailbox-controller.h lead me to believe that it was used just
> > to check if it had been completed.
> >
> > Am I allowed to use .last_tx_done() to pass information back to the
> > mailbox client? If I could, that'd certainly be a nice way to get the
> > information on whether the service failed etc.
> >
> > Hopefully that, plus when you have a chance to look at the code, will
> > make what I am asking about a little clearer!
>
> Just wondering if you've had a chance to look at this again! I know it's
> missed the merge window this time around but I would like to get this
> behaviour fixed as other work depends on it.
>
My opinion about adding a new api just to accommodate remote f/w's
behaviour change across updates is still no.
last_tx_done() is more abstract than you think -- it has to play with
dozens of behaviors of remotes. So may just wrap your whatever logic,
of "tx is done", in that.

This query within the patchset threw me off -- I thought you needed
the new api for the patchset, so I didn't look further.
Looking at it now, I am ok with applying Patches 1,2 and 3. If you want.

cheers.