Re: [PATCH] powerpc/pseries/vas: Don't print an error when VAS is unavailable

[Haren Myneni <haren@linux.ibm.com>]

On Tue, 2021-11-30 at 10:25 +1100, Michael Ellerman wrote:
> Nicholas Piggin <npiggin@gmail.com> writes:
> > Excerpts from Cédric Le Goater's message of November 26, 2021 5:13
> > pm:
> > > On 11/26/21 06:21, Nicholas Piggin wrote:
> > > > KVM does not support VAS so guests always print a useless error
> > > > on boot
> > > > 
> > > >      vas: HCALL(398) error -2, query_type 0, result buffer
> > > > 0x57f2000
> > > > 
> > > > Change this to only print the message if the error is not
> > > > H_FUNCTION.
> > > 
> > > Just being curious, why is it even called since "ibm,compression"
> > > should
> > > not be exposed in the DT ?
> > 
> > It looks like vas does not test for it. I guess in theory there can
> > be 
> > other functions than compression implemented as an accelerator.
> > Maybe
> > that's why?
> 
> Yeah I guess, or it's just not structured that well. The vas platform
> code is a bit awkward, it's there to support drivers, but it's not
> actually driver code.
> 
> I think we can probably rework it so the vas code does nothing until
> a
> driver calls in to it.
> 
> eg. something like below.

Correct, Even though NXGZIP is the only usage right now, VAS is
accelerator switchboard which should support other coprocessor types
such as GZIP and 842 or SW type solutions such as fast thread wakeup
and fast memory copy. 

So can we leave VAS initialization separate from drivers and use some
feature such as FW_FEATURE_LPAR to differentiate from KVM guests?

Thanks
Haren

> 
> cheers
> 
> 
> diff --git a/arch/powerpc/platforms/pseries/vas.c
> b/arch/powerpc/platforms/pseries/vas.c
> index b043e3936d21..dc3491fc919d 100644
> --- a/arch/powerpc/platforms/pseries/vas.c
> +++ b/arch/powerpc/platforms/pseries/vas.c
> @@ -454,6 +454,8 @@ static const struct vas_user_win_ops vops_pseries
> = {
>  	.close_win	= vas_deallocate_window, /* Close window */
>  };
>  
> +static int pseries_vas_init(void);
> +
>  /*
>   * Supporting only nx-gzip coprocessor type now, but this API code
>   * extended to other coprocessor types later.
> @@ -463,7 +465,8 @@ int vas_register_api_pseries(struct module *mod,
> enum vas_cop_type cop_type,
>  {
>  	int rc;
>  
> -	if (!copypaste_feat)
> +	rc = pseries_vas_init();
> +	if (rc || !copypaste_feat)
>  		return -ENOTSUPP;
>  
>  	rc = vas_register_coproc_api(mod, cop_type, name,
> &vops_pseries);
> @@ -531,7 +534,7 @@ static int get_vas_capabilities(u8 feat, enum
> vas_cop_feat_type type,
>  	return 0;
>  }
>  
> -static int __init pseries_vas_init(void)
> +static int pseries_vas_init(void)
>  {
>  	struct hv_vas_cop_feat_caps *hv_cop_caps;
>  	struct hv_vas_all_caps *hv_caps;
> @@ -592,4 +595,3 @@ static int __init pseries_vas_init(void)
>  	kfree(hv_caps);
>  	return rc;
>  }
> -machine_device_initcall(pseries, pseries_vas_init);