Re: [PATCH v2] ipmi: looped device detection

[Corey Minyard]

On 09/18/2018 01:42 PM, Patrick Venture wrote:
> On Wed, Sep 12, 2018 at 3:54 PM Patrick Venture <venture@xxxxxxxxxx> wrote:
> > On Wed, Sep 12, 2018 at 3:10 PM Corey Minyard <minyard@xxxxxxx> 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.

I'm ok with doing this, but I lied about the patch being fine, there are 
some issue.
Well, I didn't lie, but I didn't look closely enough.

Can you use dev_xxx() instead of pr_xxx(). I know the driver isn't 
currently
consistent, but there are a number of patches I have pending to make it
better and it's a longer-term goal.

Can you make GET_DEVICE_ID_ATTEMPTS more specific, add IPMI_SI_ to
the beginning or something.

I am not sure that I'm ok with waiting up to 1.25 seconds in the init 
function.
As I mentioned before, a large number of systems have broken ACPI/SMBIOS
information, and for those it will add 1.25 seconds to the boot time of 
every
one of those systems. That won't make me a popular guy :-).

This is a harder problem to figure out what to do. To solve it properly 
would
mean having a timer or thread drive this, and unload the module later if
the process fails.

-corey

> 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@xxxxxxxxxx>
> > > > ---
> > > > 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,