Re: [PATCH] mmc: Try power cycling card if command request times out

[Ulf Hansson]

On Thu, 4 Mar 2021 at 14:48, Marten Lindahl <martenli@xxxxxxxx> wrote:
>
> Hi Ulf! My apologies for the delay.
>
> On Tue, Mar 02, 2021 at 09:45:02AM +0100, Ulf Hansson wrote:
> > On Mon, 1 Mar 2021 at 22:59, Marten Lindahl <martenli@xxxxxxxx> wrote:
> > >
> > > Hi Ulf!
> > >
> > > Thank you for your comments!
> > >
> > > On Mon, Mar 01, 2021 at 09:50:56AM +0100, Ulf Hansson wrote:
> > > > + Adrian
> > > >
> > > > On Tue, 16 Feb 2021 at 23:43, Mårten Lindahl <marten.lindahl@xxxxxxxx> wrote:
> > > > >
> > > > > Sometimes SD cards that has been run for a long time enters a state
> > > > > where it cannot by itself be recovered, but needs a power cycle to be
> > > > > operational again. Card status analysis has indicated that the card can
> > > > > end up in a state where all external commands are ignored by the card
> > > > > since it is halted by data timeouts.
> > > > >
> > > > > If the card has been heavily used for a long time it can be weared out,
> > > > > and should typically be replaced. But on some tests, it shows that the
> > > > > card can still be functional after a power cycle, but as it requires an
> > > > > operator to do it, the card can remain in a non-operational state for a
> > > > > long time until the problem has been observed by the operator.
> > > > >
> > > > > This patch adds function to power cycle the card in case it does not
> > > > > respond to a command, and then resend the command if the power cycle
> > > > > was successful. This procedure will be tested 1 time before giving up,
> > > > > and resuming host operation as normal.
> > > >
> > > > I assume the context above is all about the ioctl interface?
> > > >
> > >
> > > Yes, that's correct. The problem we have seen is triggered by ioctls.
> > >
> > > > So, when the card enters this non functional state, have you tried
> > > > just reading a block through the regular I/O interface. Does it
> > > > trigger a power cycle of the card - and then makes it functional
> > > > again?
> > > >
> > >
> > > Yes, we have tried that, and it does trigger a power cycle, making the card
> > > operational again. But as it requires an operator to trigger it, I thought
> > > it might be something that could be automated here. At least once.
> >
> > Not sure what you mean by operator here? In the end it's a userspace
> > program running and I assume it can deal with error paths. :-)
> >
> > In any case, I understand your point.
> >
>
> Yes, we have a userspace program. So if the userspace program will try to
> restore the card in a situation such as the one we are trying to solve
> here, how shall it perform it? Is it expected that a ioctl CMD0 request
> should be enough, or is there any other support for a userspace program to
> reset the card?

Correct, there is no way for userspace to reset cards through an ioctl.

>
> If it falls on a ioctl command to reset the card, how do we handle the case
> where the ioctl times out anyway? Or is the only way for a userspace program
> to restore the card, to make a block transfer that fails?

Yes, that is what I was thinking. According to the use case you have
described, this should be possible for you to implement as a part of
your userspace program, no?

[...]

Kind regards
Uffe