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

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Mar 08, 2026 at 10:46:31PM +0100, Jori Koolstra wrote:
> The class_create() call has been deprecated in favor of class_register()
> as the driver core now allows for a struct class to be in read-only
> memory.
> 
> In vas_register_coproc_api() the dynamic allocation of the struct class
> corresonding to the coprocessor type (right now only nx-gzip) is
> replaced by calling
> 
> 	static const struct class* cop_to_class(enum vas_cop_type cop)
> 
> which links the coprocessor type to the appropriate static const struct
> class.
> 
> Compile tested only.
> 
> Link: https://lore.kernel.org/all/2023040244-duffel-pushpin-f738@gregkh/
> 
> Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
> ---
> v2: undo whitespace removal
> 
>  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?

thanks,

greg k-h