Re: [PATCH] drm/i915/gt: Continue creating engine sysfs files even after a failure

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Mon, Aug 19, 2024 at 01:31:40PM +0200, Andi Shyti wrote:
> The i915 driver generates sysfs entries for each engine of the
> GPU in /sys/class/drm/cardX/engines/.
> 
> The process is straightforward: we loop over the UABI engines and
> for each one, we:
> 
>  - Create the object.
>  - Create basic files.
>  - If the engine supports timeslicing, create timeslice duration files.
>  - If the engine supports preemption, create preemption-related files.
>  - Create default value files.
> 
> Currently, if any of these steps fail, the process stops, and no
> further sysfs files are created.
> 
> However, it's not necessary to stop the process on failure.
> Instead, we can continue creating the remaining sysfs files for
> the other engines. Even if some files fail to be created, the
> list of engines can still be retrieved by querying i915.
> 
> Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>

Uh, sysfs is uapi. Either we need it, and it _must_ be there, or it's not
needed, and we should delete those files probably.

This is different from debugfs, where failures are consistently ignored
because that's the conscious design choice Greg made and wants supported.
Because debugfs is optional.

So please make sure we correctly fail driver load if these don't register.
Even better would be if sysfs files are registered atomically as attribute
blocks, but that's an entire different can of worms. But that would really
clean up this code and essentially put any failure handling onto core
driver model and sysfs code.
-Sima

> ---
> Hi,
> 
> It might make sense to create an "inv-<engine_name>" if something
> goes wrong, so that the user is aware that the engine exists, but
> the sysfs file is not present.
> 
> One further improvement would be to provide more information
> about thei failure reason the dev_warn() message.
> 
> Andi
> 
>  drivers/gpu/drm/i915/gt/sysfs_engines.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/sysfs_engines.c b/drivers/gpu/drm/i915/gt/sysfs_engines.c
> index 021f51d9b456..aab2759067d2 100644
> --- a/drivers/gpu/drm/i915/gt/sysfs_engines.c
> +++ b/drivers/gpu/drm/i915/gt/sysfs_engines.c
> @@ -530,9 +530,8 @@ void intel_engines_add_sysfs(struct drm_i915_private *i915)
>  err_object:
>  			kobject_put(kobj);
>  err_engine:
> -			dev_err(kdev, "Failed to add sysfs engine '%s'\n",
> -				engine->name);
> -			break;
> +			dev_warn(kdev, "Failed to add sysfs engine '%s'\n",
> +				 engine->name);
>  		}
>  	}
>  }
> -- 
> 2.45.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch