Re: [PATCH v10 08/26] gunyah: rsc_mgr: Add resource manager RPC core

[Elliot Berman]

On 2/16/2023 11:37 PM, Greg Kroah-Hartman wrote:
> On Thu, Feb 16, 2023 at 09:40:52AM -0800, Elliot Berman wrote:
> > On 2/15/2023 10:43 PM, Greg Kroah-Hartman wrote:
> > > On Tue, Feb 14, 2023 at 01:23:25PM -0800, Elliot Berman wrote:
> > > > +struct gh_rm {
> > > > +	struct device *dev;
> > >
> > > What device does this point to?
> >
> > The platform device.
>
> What platform device?  And why a platform device?

This will be used for the dev_printk. It's presently also used for the 
reference counting. From your comments below, I'll switch the reference 
counting away from this platform device.

> > > > +	struct gunyah_resource tx_ghrsc, rx_ghrsc;
> > > > +	struct gh_msgq msgq;
> > > > +	struct mbox_client msgq_client;
> > > > +	struct gh_rm_connection *active_rx_connection;
> > > > +	int last_tx_ret;
> > > > +
> > > > +	struct idr call_idr;
> > > > +	struct mutex call_idr_lock;
> > > > +
> > > > +	struct kmem_cache *cache;
> > > > +	struct mutex send_lock;
> > > > +	struct blocking_notifier_head nh;
> > > > +};
> > >
> > > This obviously is the "device" that your system works on, so what are
> > > the lifetime rules of it?  Why isn't is just a real 'struct device' in
> > > the system instead of a random memory blob with a pointer to a device?
> > >
> > > What controls the lifetime of this structure and where is the reference
> > > counting logic for it?
> >
> > The lifetime of the structure is bound by the platform device that above
> > struct device *dev points to. get_gh_rm and put_gh_rm increments the device
> > ref counter and ensures lifetime of the struct is also extended.
>
> But this really is "your" device, not the platform device.  So make it a
> real one please as that is how the kernel's driver model works.  Don't
> hang "magic structures" off of a random struct device and have them
> control the lifetime rules of the parent without actually being a device
> themself.  This should make things simpler overall, not more complex,
> and allow you to expose things to userspace properly (right now your
> data is totally hidden.)

The "real" device I create here is the miscdev, so I think the 
recommendation here is to do refcounting off that miscdev. Is this the 
approach you were thinking of?

Thanks,
Elliot