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SubjectRe: [PATCH v2] ipmi: looped device detection
On Wed, Sep 12, 2018 at 3:54 PM Patrick Venture <venture@google.com> wrote:
>
> On Wed, Sep 12, 2018 at 3:10 PM Corey Minyard <minyard@acm.org> wrote:
> >
> > On 09/11/2018 05:56 PM, Patrick Venture wrote:
> > > Try to get the device ID repeatedly during initialization before giving up.
> > > The BMC isn't always responsive, and this allows it to be slightly flaky
> > > during early boot.
> > >
> > > Tested: Installed on a system with the BMC software disabled
> > > such that it was non-responsive. The driver correctly detected this
> > > and gave up as expected. Then I re-enabled the BMC software unloaded
> > > and reloaded the driver and it was detected properly.
> >
> > The patch looks fine, but I wonder if this is something that is really
> > valuable.
> > I have wondered about this before.
> >
> > The question is: If the BMC is unavailable, what are the chances of it
> > becoming
> > available by the time you do 5 attempts? I would guess that is a pretty
> > small
> > chance, which is why I haven't done this already.

Friendly ping. I'd like to get a sense of whether you're likely to
accept this. If not, it's fine, will close out patch in current
downstream rebase.

Thanks

>
> This patch was actually critical for us to provide a reliable IPMI
> interface. The version of OpenBMC or the state of the BMC at the
> point the kernel was loading was flaky, so following the example in
> the BIOS source, we just re-try a few times. We also can hold boot X
> seconds until it's responding, but, this avoided some issues inherent
> with that.
>
> >
> > You could have something that re-tested periodically, but there are so many
> > systems with IPMI specified in ACPI or SMBIOS that is wrong, and it would
> > try forever. Also not really a good thing.
>
> If we did a periodic check, it could check X times, but I felt going
> for a simple solution was ideal -- and this idea was proved out on a
> few platforms. We have other drivers that are loaded by the kernel
> (not at run-time) and they depend on IPMI, and without this patch they
> would then have a non-trivial probability of failure.
>
> >
> > So I've left it to reload the driver or use the hotmod interface.
> >
> > -corey
> >
> > > Signed-off-by: Patrick Venture <venture@google.com>
> > > ---
> > > v2:
> > > - removed extra variable that was set but not used.
> > > ---
> > > drivers/char/ipmi/ipmi_si_intf.c | 23 ++++++++++++++++++++++-
> > > 1 file changed, 22 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
> > > index 90ec010bffbd..5fed96897fe8 100644
> > > --- a/drivers/char/ipmi/ipmi_si_intf.c
> > > +++ b/drivers/char/ipmi/ipmi_si_intf.c
> > > @@ -1918,11 +1918,13 @@ int ipmi_si_add_smi(struct si_sm_io *io)
> > > * held, primarily to keep smi_num consistent, we only one to do these
> > > * one at a time.
> > > */
> > > +#define GET_DEVICE_ID_ATTEMPTS 5
> > > static int try_smi_init(struct smi_info *new_smi)
> > > {
> > > int rv = 0;
> > > int i;
> > > char *init_name = NULL;
> > > + unsigned long sleep_rm;
> > >
> > > pr_info(PFX "Trying %s-specified %s state machine at %s address 0x%lx, slave address 0x%x, irq %d\n",
> > > ipmi_addr_src_to_str(new_smi->io.addr_source),
> > > @@ -2003,7 +2005,26 @@ static int try_smi_init(struct smi_info *new_smi)
> > > * Attempt a get device id command. If it fails, we probably
> > > * don't have a BMC here.
> > > */
> > > - rv = try_get_dev_id(new_smi);
> > > + for (i = 0; i < GET_DEVICE_ID_ATTEMPTS; i++) {
> > > + pr_info(PFX "Attempting to read BMC device ID\n");
> > > + rv = try_get_dev_id(new_smi);
> > > + /* If it succeeded, stop trying */
> > > + if (!rv)
> > > + break;
> > > +
> > > + /* Sleep for ~0.25s before trying again instead of hammering
> > > + * the BMC.
> > > + */
> > > + sleep_rm = msleep_interruptible(250);
> > > + if (sleep_rm != 0) {
> > > + pr_info(PFX "Find BMC interrupted\n");
> > > + rv = -EINTR;
> > > + goto out_err;
> > > + }
> > > + }
> > > +
> > > + /* If we exited the loop above and rv is non-zero we ran out of tries.
> > > + */
> > > if (rv) {
> > > if (new_smi->io.addr_source)
> > > dev_err(new_smi->io.dev,
> >
> >

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