Re: [PATCH v1 2/5] driver core: Set deferred probe reason when deferred by driver core

[Saravana Kannan <saravanak@google.com>]

On Tue, Sep 14, 2021 at 12:01 AM Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
>
> Hi Saravana,
>
> On Tue, Sep 14, 2021 at 6:39 AM Saravana Kannan <saravanak@google.com> wrote:
> > When the driver core defers the probe of a device, set the deferred
> > probe reason so that it's easier to debug. The deferred probe reason is
> > available in debugfs under devices_deferred.
> >
> > Signed-off-by: Saravana Kannan <saravanak@google.com>
>
> Thanks for your patch!

Thanks for the reviews!

>
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -955,6 +955,29 @@ static void device_links_missing_supplier(struct device *dev)
> >         }
> >  }
> >
> > +/**
> > + * dev_set_def_probe_reason - Set the deferred probe reason for a device
> > + * @dev: the pointer to the struct device
> > + * @fmt: printf-style format string
> > + * @...: arguments as specified in the format string
> > + *
> > + * This is a more caller-friendly version of device_set_deferred_probe_reason()
> > + * that takes variable argument inputs similar to dev_info().
> > + */
> > +static void dev_set_def_probe_reason(const struct device *dev, const char *fmt, ...)
>
> So this is indeed similar to device_set_deferred_probe_reason(),
> but the function's name is completely different, unlike e.g.
> (v)printf()?

Yes.

>
> > +{
> > +       struct va_format vaf;
> > +       va_list args;
> > +
> > +       va_start(args, fmt);
> > +       vaf.fmt = fmt;
> > +       vaf.va = &args;
> > +
> > +       device_set_deferred_probe_reason(dev, &vaf);
> > +
> > +       va_end(args);
> > +}
>
> I think you can just make this a macro wrapper calling
> dev_err_probe(dev, -EPROBE_DEFER, fmt, ...).
> Or open-code that below.

Good point. I think I can make it be a wrapper macro.

>
> > +
> >  /**
> >   * device_links_check_suppliers - Check presence of supplier drivers.
> >   * @dev: Consumer device.
> > @@ -975,6 +998,7 @@ int device_links_check_suppliers(struct device *dev)
> >  {
> >         struct device_link *link;
> >         int ret = 0;
> > +       struct fwnode_handle *sup_fw;
> >
> >         /*
> >          * Device waiting for supplier to become available is not allowed to
> > @@ -983,10 +1007,13 @@ int device_links_check_suppliers(struct device *dev)
> >         mutex_lock(&fwnode_link_lock);
> >         if (dev->fwnode && !list_empty(&dev->fwnode->suppliers) &&
> >             !fw_devlink_is_permissive()) {
> > +               sup_fw = list_first_entry(&dev->fwnode->suppliers,
> > +                                         struct fwnode_link,
> > +                                         c_hook)->supplier;
> >                 dev_dbg(dev, "probe deferral - wait for supplier %pfwP\n",
> > -                       list_first_entry(&dev->fwnode->suppliers,
> > -                       struct fwnode_link,
> > -                       c_hook)->supplier);
> > +                       sup_fw);
> > +               dev_set_def_probe_reason(dev,
> > +                       "wait for supplier %pfwP\n", sup_fw);
>
> dev_err_probe() would replace both the dev_dbg() and the
> dev_set_def_probe_reason().

I intentionally didn't use dev_err_probe() because:

1. I wanted the messages to be a bit different -- not have the "probe
deferral" in the deferred_devices file but have it in the dmesg logs
so that the log is clearer.
2. And more importantly, I'm working on a patch (could take a few
weeks) that'll make this place return -EPROBE_DEFER vs -ENODEV (or
whatever) for different situations. And using dev_err_probe() with
-ENODEV would cause it to print the error (when I don't want it to).
And always doing dev_err_probe(dev, -EPROBE_DEFER,...) while returning
-ENODEV would be confusing.

>
> >                 mutex_unlock(&fwnode_link_lock);
> >                 return -EPROBE_DEFER;
> >         }
> > @@ -1003,6 +1030,9 @@ int device_links_check_suppliers(struct device *dev)
> >                         device_links_missing_supplier(dev);
> >                         dev_dbg(dev, "probe deferral - supplier %s not ready\n",
> >                                 dev_name(link->supplier));
> > +                       dev_set_def_probe_reason(dev,
> > +                               "supplier %s not ready\n",
> > +                               dev_name(link->supplier));
>
> Likewise.

Same reason as above.

I mainly added you for comments on 5/5. Hopefully you'll have some
comments on that too by the time I'm up tomorrow :)

-Saravana

>
> >                         ret = -EPROBE_DEFER;
> >                         break;
> >                 }
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds