Re: [PATCH v3 4/6] drm/xe/configfs: Allow to select by class only

[Raag Jadav <raag.jadav@intel.com>]

On Fri, Sep 05, 2025 at 10:50:32PM -0700, Lucas De Marchi wrote:
> For a future configfs attribute, it's desirable to select by engine mask
> only as the instance doesn't make sense.
> 
> Rename the function lookup_engine_mask() to lookup_engine_info() and
> make it return the entry. This allows parse_engine() to still return an
> item if the caller wants to allow parsing a class-only string like
> "rcs", "bcs", "ccs", etc.

...

> -static bool lookup_engine_mask(const char *pattern, u64 *mask)
> +/*
> + * Lookup engine_info. If @mask is not NULL, reduce the mask according to the
> + * instance in @pattern.
> + *
> + * Examples of inputs:
> + * - lookup_engine_info("rcs0", &mask): return "rcs" entry from @engine_info and
> + *   mask == BIT_ULL(XE_HW_ENGINE_RCS0)
> + * - lookup_engine_info("rcs*", &mask): return "rcs" entry from @engine_info and
> + *   mask == XE_HW_ENGINE_RCS_MASK
> + * - lookup_engine_info("rcs", NULL): return "rcs" entry from @engine_info
> + */
> +static const struct engine_info *lookup_engine_info(const char *pattern, u64 *mask)

Now that we're returning engine_info, I'm wondering if we have any use for
mask parameter?

Raag

>  {
>  	for (size_t i = 0; i < ARRAY_SIZE(engine_info); i++) {
>  		u8 instance;
> @@ -263,29 +275,33 @@ static bool lookup_engine_mask(const char *pattern, u64 *mask)
>  			continue;
>  
>  		pattern += strlen(engine_info[i].cls);
> +		if (!mask && !*pattern)
> +			return &engine_info[i];
>  
>  		if (!strcmp(pattern, "*")) {
>  			*mask = engine_info[i].mask;
> -			return true;
> +			return &engine_info[i];
>  		}
>  
>  		if (kstrtou8(pattern, 10, &instance))
> -			return false;
> +			return NULL;
>  
>  		bit = __ffs64(engine_info[i].mask) + instance;
>  		if (bit >= fls64(engine_info[i].mask))
> -			return false;
> +			return NULL;
>  
>  		*mask = BIT_ULL(bit);
> -		return true;
> +		return &engine_info[i];
>  	}
>  
> -	return false;
> +	return NULL;
>  }