Re: [PATCH 2/7] mfd / platform: cros_ec: move lightbar attributes to its own driver.

[Guenter Roeck]

On 11/23/18 3:52 AM, Enric Balletbo i Serra wrote:
> Hi Guenter,
>
> On 22/11/18 18:41, Guenter Roeck wrote:
> > Hi Enric,
> >
> > On Thu, Nov 22, 2018 at 12:33:51PM +0100, Enric Balletbo i Serra wrote:
> > > The entire way how cros sysfs attibutes are created is broken.
> > > cros_ec_lightbar should be its own driver and its attributes should be
> > > associated with a lightbar driver not the mfd driver. In order to retain
> > > the path, the lightbar attributes are attached to the cros_class.
> > >
> > > The patch also adds the sysfs documentation.
> > >
> > > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> > > ---
> > ...
> > >   
> > > +int cros_ec_attach_attribute_group(struct cros_ec_dev *ec,
> > > +				   struct attribute_group *attrs)
> > > +{
> > > +	return sysfs_create_group(&ec->class_dev.kobj, attrs);
> > > +}
> > > +EXPORT_SYMBOL(cros_ec_attach_attribute_group);
> > > +
> > > +void cros_ec_detach_attribute_group(struct cros_ec_dev *ec,
> > > +				    struct attribute_group *attrs)
> > > +{
> > > +	sysfs_remove_group(&ec->class_dev.kobj, attrs);
> > > +}
> > > +EXPORT_SYMBOL(cros_ec_detach_attribute_group);
> > > +
> >
> > Are those two functions necessary ? Why not just call sysfs_create_group
> > and sysfs_remove_group directly from the calling code ?
>
> Actually we have cros_ec_dev which registers the cros_ec class, and sysfs/vbc
> and lightbar using this cros_ec class. I had problems unloading the different
> modules. For example, when I removed cros_ec_dev modules before
> cros_ec_sysfs/cros_ec_vbc/cros_ec_lightbar I got a hang.
>
> To solve the hang I did the easy solution that is make these drivers depend on
> cros_ec_dev so you're not able to unload cros_ec_dev if first you don't unload
> the sysfs/vbc/lightbar.

That seems like a side effect of the callbacks, which may increase the use count
of cros_ec_dev. If the lack of these callbacks causes problems, we should identify
the root cause and fix it, and not depend on side effects of a callback.

Thanks,
Guenter

> Thinking again about it, I don't really understand now why failed in the first
> place, cros_ec_dev is the parent, so, on remove should call mfd_remove_devices
> for the subdevices.
>
> So, let me check again this and I'll back to you.
>
> Thanks,
>   Enric
>
>
> > Thanks,
> > Guenter