Re: [PATCH v2] powerpc: vas-api: constify dynamic struct class in coproc api register

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 09, 2026 at 11:48:57AM +0100, Jori Koolstra wrote:
> My bad, the earlier email went out to soon.
> 
> > Op 09-03-2026 07:01 CET schreef Greg KH <gregkh@linuxfoundation.org>:
> > >  arch/powerpc/platforms/book3s/vas-api.c | 34 +++++++++++++++++++------
> > >  1 file changed, 26 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
> > > index ea4ffa63f043..e377981fd533 100644
> > > --- a/arch/powerpc/platforms/book3s/vas-api.c
> > > +++ b/arch/powerpc/platforms/book3s/vas-api.c
> > > @@ -45,7 +45,7 @@ static struct coproc_dev {
> > >  	struct device *device;
> > >  	char *name;
> > >  	dev_t devt;
> > > -	struct class *class;
> > > +	const struct class *class;
> > >  	enum vas_cop_type cop_type;
> > >  	const struct vas_user_win_ops *vops;
> > >  } coproc_device;
> > > @@ -599,6 +599,21 @@ static struct file_operations coproc_fops = {
> > >  	.unlocked_ioctl = coproc_ioctl,
> > >  };
> > >  
> > > +static const struct class nx_gzip_class = {
> > > +	.name		= "nx-gzip",
> > > +	.devnode	= coproc_devnode
> > > +};
> > > +
> > > +static const struct class* cop_to_class(enum vas_cop_type cop)
> > > +{
> > > +	switch (cop) {
> > > +	case VAS_COP_TYPE_GZIP:		return &nx_gzip_class;
> > > +	default:
> > > +		pr_err("No device class defined for cop type %d\n", cop);
> > > +		return NULL;
> > > +	}
> > > +}
> > > +
> > >  /*
> > >   * Supporting only nx-gzip coprocessor type now, but this API code
> > >   * extended to other coprocessor types later.
> > > @@ -609,6 +624,10 @@ int vas_register_coproc_api(struct module *mod, enum vas_cop_type cop_type,
> > >  {
> > >  	int rc = -EINVAL;
> > >  	dev_t devno;
> > > +	const struct class* class = cop_to_class(cop_type);
> > > +
> > > +	if (!class)
> > > +		return rc;
> > 
> > How can this happen?
> > 
> > This feels odd, are different types of devices being registered here?  I
> > don't see where VAS_COP_TYPE_GZIP was being tested in the original code,
> > why add this additional logic?
> > 
> 
> My line of thought is this:
> 
> There is a function vas_register_coproc_api() that does some kind of registering
> for different coprocessor types. It has the following comment above:
> 
> /*
>  * Supporting only nx-gzip coprocessor type now, but this API code
>  * extended to other coprocessor types later.
>  */

I guess "later" never happened :(

> If you look at where this function is eventually triggered it is indeed only ever
> passed VAS_COP_TYPE_GZIP. For instance, line 1238 of drivers/crypto/nx/nx-common-series.c
> has the call
> 
> 	ret = vas_register_api_pseries(THIS_MODULE, VAS_COP_TYPE_GZIP,
> 				       "nx-gzip");
> 
> (which immediately calls vas_register_coproc_api())
> 
> It also passes a hard-coded name for the device ("nx-gzip"), and this name is also
> used as the device class name. Now, this is a problem if we want to get rid of
> class_create(). Somehow "nx-gzip" needs to get linked to the appropriate const struct
> class. I figured it is better to use the cop_type, and a cop_to_class() function to
> set this link. However, since the other co-processor types are not implemented (yet)
> it would seem silly to already assign struct classes for these, hence the NULL return.
> It is meant to signal: not implemented. Then again, if ever a new co-processor was added
> you must update the cop_to_class()... but at least this is my line of thought.
> 
> There is also a function static char *cop_to_str(int cop) that strangely takes
> an int instead of an enum vas_cop_type, and also misses an option I think.

Ok, I'll defer to the maintainer here, as it's their code, and seems to
not follow the "normal" style of handling classes.

thanks,

greg k-h