[PATCH v2 1/3] drm/i915/gt: Support fixed CCS mode

[Joonas Lahtinen]

Quoting Tvrtko Ursulin (2024-01-05 12:39:31)
> 
> On 04/01/2024 21:23, Andi Shyti wrote:

<SNIP>

> >>> +void intel_gt_apply_ccs_mode(struct intel_gt *gt)
> >>> +{
> >>> +   mutex_lock(&gt->ccs.mutex);
> >>> +   __intel_gt_apply_ccs_mode(gt);
> >>> +   mutex_unlock(&gt->ccs.mutex);
> >>> +}
> >>> +
> >>> +void intel_gt_init_ccs_mode(struct intel_gt *gt)
> >>> +{
> >>> +   mutex_init(&gt->ccs.mutex);
> >>> +   gt->ccs.mode = 1;
> >>
> >> What is '1'? And this question carries over to the sysfs interface in the
> >> following patch - who will use it and where it is documented how to use it?
> > 
> > The value '1' is explained in the comment above[1] and in the
> 
> Do you mean this is mode '1':
> 
>   * With 1 engine (ccs0):
>   *   slice 0, 1, 2, 3: ccs0
> 
> ?
> 
> But I don't see where it says what do different modes mean on different 
> SKU configurations.
> 
> It also does not say what should the num_slices sysfs file be used for.
> 
> Does "mode N" mean "assign each command streamer N compute slices"? Or 
> "assign each compute slice N command streamers"?
> 
> I wonder if we should add something user friendly into 
> Documentation/ABI/*/sysfs-... Joonas your thoughts?

We definitely should always properly document all sysfs additions, just
seems like we less frequently remember to do so. So yeah, this should be
documented just like other uAPI.

I also like the idea of not exposing the the file at all if the value
can't be modified.

The ccs_mode is just supposed to allow user to select how many CCS
engines they want to expose, and always make an even split of slices
between them, nothing more nothing less.

Regards, Joonas