Re: [Intel-gfx] [PATCH] drm/i915/gsc: Assign a uabi class number to the GSC CS

[Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>]

On 11/10/2023 4:00 AM, Tvrtko Ursulin wrote:
>
> On 09/11/2023 23:53, Daniele Ceraolo Spurio wrote:
>> The GSC CS is not exposed to the user, so we skipped assigning a uabi
>> class number for it. However, the trace logs use the uabi class and
>> instance to identify the engine, so leaving uabi class unset makes the
>> GSC CS show up as the RCS in those logs.
>> Given that the engine is not exposed to the user, we can't add a new
>> case in the uabi enum, so we insted internally define a kernel
>> reserved class using the next free number.
>>
>> Fixes: 194babe26bdc ("drm/i915/mtl: don't expose GSC command streamer 
>> to the user")
>> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
>> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
>> Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
>> Cc: Matt Roper <matthew.d.roper@intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_engine_user.c | 17 ++++++++---------
>>   drivers/gpu/drm/i915/gt/intel_engine_user.h |  4 ++++
>>   drivers/gpu/drm/i915/i915_drm_client.h      |  2 +-
>>   drivers/gpu/drm/i915/i915_drv.h             |  2 +-
>>   4 files changed, 14 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c 
>> b/drivers/gpu/drm/i915/gt/intel_engine_user.c
>> index 118164ddbb2e..3fd32bedd6e7 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
>> @@ -47,6 +47,7 @@ static const u8 uabi_classes[] = {
>>       [VIDEO_DECODE_CLASS] = I915_ENGINE_CLASS_VIDEO,
>>       [VIDEO_ENHANCEMENT_CLASS] = I915_ENGINE_CLASS_VIDEO_ENHANCE,
>>       [COMPUTE_CLASS] = I915_ENGINE_CLASS_COMPUTE,
>> +    [OTHER_CLASS] = I915_KERNEL_RSVD_CLASS,
>
> Could we set it to -1 (aka no uabi class) to avoid needing to maintain 
> the new macros?
>
> And then just teach intel_engines_driver_register to skip -1. Would 
> also need teaching engine_rename to handle -1.
>
> Might end up a smaller and more maintainable patch - worth a try do 
> you think?

That was my initial idea as well, but the issue with this approach is 
the engine_uabi_class_count[] array, which is sized based on the number 
of uabi classes, so having class -1 would needlessly increase its size a 
lot even when using a u8. I thought about limiting the class entry to 3 
bits so the array would max out at 8 entries, but that seemed to be 
getting a bit too convoluted. I can give it a go if you think it's be 
cleaner overall.

Note that this patch does not introduce any new macros that would need 
to be maintained. I915_LAST_UABI_ENGINE_CLASS already existed (I just 
moved it from one file to another) and is the only one that changes when 
a new "real" uabi class is added; the other defines are based on this 
one. This also implies that if a new uabi class is added then 
I915_KERNEL_RSVD_CLASS would be bumped to the next free number, which 
would cause the GSC to show as a different uabi class in newer logs; 
considering that i915 is on its way out, a new class seems very unlikely 
so I thought it'd be an acceptable compromise to keep things simple.

>
>>   };
>>     static int engine_cmp(void *priv, const struct list_head *A,
>> @@ -138,7 +139,7 @@ const char *intel_engine_class_repr(u8 class)
>>           [COPY_ENGINE_CLASS] = "bcs",
>>           [VIDEO_DECODE_CLASS] = "vcs",
>>           [VIDEO_ENHANCEMENT_CLASS] = "vecs",
>> -        [OTHER_CLASS] = "other",
>> +        [OTHER_CLASS] = "gsc",
>
> Maybe unrelated?

no. Before this patch, we hardcoded "gsc" below when calling 
engine_rename() for it. With this patch, we use the name from this 
array, so it needs to be updated. The GEM_WARN_ON below was added to 
make sure we don't get different engines in OTHER_CLASS that might not 
match the "gsc" naming.

Daniele

>
> Regards,
>
> Tvrtko
>
>>           [COMPUTE_CLASS] = "ccs",
>>       };
>>   @@ -216,14 +217,8 @@ void intel_engines_driver_register(struct 
>> drm_i915_private *i915)
>>           if (intel_gt_has_unrecoverable_error(engine->gt))
>>               continue; /* ignore incomplete engines */
>>   -        /*
>> -         * We don't want to expose the GSC engine to the users, but we
>> -         * still rename it so it is easier to identify in the debug 
>> logs
>> -         */
>> -        if (engine->id == GSC0) {
>> -            engine_rename(engine, "gsc", 0);
>> -            continue;
>> -        }
>> +        /* The only engine we expect in OTHER_CLASS is GSC0 */
>> +        GEM_WARN_ON(engine->class == OTHER_CLASS && engine->id != 
>> GSC0);
>>             GEM_BUG_ON(engine->class >= ARRAY_SIZE(uabi_classes));
>>           engine->uabi_class = uabi_classes[engine->class];
>> @@ -238,6 +233,10 @@ void intel_engines_driver_register(struct 
>> drm_i915_private *i915)
>>                     intel_engine_class_repr(engine->class),
>>                     engine->uabi_instance);
>>   +        /* We don't want to expose the GSC engine to the users */
>> +        if (engine->id == GSC0)
>> +            continue;
>> +
>>           rb_link_node(&engine->uabi_node, prev, p);
>>           rb_insert_color(&engine->uabi_node, &i915->uabi_engines);
>>   diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.h 
>> b/drivers/gpu/drm/i915/gt/intel_engine_user.h
>> index 3dc7e8ab9fbc..dd31805b2a5a 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_engine_user.h
>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.h
>> @@ -11,6 +11,10 @@
>>   struct drm_i915_private;
>>   struct intel_engine_cs;
>>   +#define I915_LAST_UABI_ENGINE_CLASS I915_ENGINE_CLASS_COMPUTE
>> +#define I915_KERNEL_RSVD_CLASS (I915_LAST_UABI_ENGINE_CLASS + 1)
>> +#define I915_MAX_UABI_CLASSES (I915_KERNEL_RSVD_CLASS + 1)
>> +
>>   struct intel_engine_cs *
>>   intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, 
>> u8 instance);
>>   diff --git a/drivers/gpu/drm/i915/i915_drm_client.h 
>> b/drivers/gpu/drm/i915/i915_drm_client.h
>> index 67816c912bca..c42cb2511348 100644
>> --- a/drivers/gpu/drm/i915/i915_drm_client.h
>> +++ b/drivers/gpu/drm/i915/i915_drm_client.h
>> @@ -12,7 +12,7 @@
>>     #include <uapi/drm/i915_drm.h>
>>   -#define I915_LAST_UABI_ENGINE_CLASS I915_ENGINE_CLASS_COMPUTE
>> +#include "gt/intel_engine_user.h"
>>     struct drm_file;
>>   struct drm_printer;
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h 
>> b/drivers/gpu/drm/i915/i915_drv.h
>> index f3be9033a93f..a718b4cb5a2d 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -238,7 +238,7 @@ struct drm_i915_private {
>>           struct list_head uabi_engines_list;
>>           struct rb_root uabi_engines;
>>       };
>> -    unsigned int engine_uabi_class_count[I915_LAST_UABI_ENGINE_CLASS 
>> + 1];
>> +    unsigned int engine_uabi_class_count[I915_MAX_UABI_CLASSES];
>>         /* protects the irq masks */
>>       spinlock_t irq_lock;