Re: [PATCH v3 5/7] drm/panfrost: Add a new ioctl to submit batches

[Alyssa Rosenzweig <alyssa@collabora.com>]

```
> +/* Syncobj reference passed at job submission time to encode explicit
> + * input/output fences.
> + */
> +struct drm_panfrost_syncobj_ref {
> +	__u32 handle;
> +	__u32 pad;
> +	__u64 point;
> +};
```

What is handle? What is point? Why is there padding instead of putting
point first?

```
>  #define PANFROST_BO_REF_EXCLUSIVE	0x1
> +#define PANFROST_BO_REF_NO_IMPLICIT_DEP	0x2
```

This seems logically backwards. NO_IMPLICIT_DEP makes sense if we're
trying to keep backwards compatibility, but here you're crafting a new
interface totally from scratch. If anything, isn't BO_REF_IMPLICIT_DEP
the flag you'd want?

```
> +	/**
> +	 * Stride of the jobs array (needed to ease extension of the
> +	 * BATCH_SUBMIT ioctl). Should be set to
> +	 * sizeof(struct drm_panfrost_job).
> +	 */
> +	__u32 job_stride;
...
> +	/**
> +	 * Stride of the BO and syncobj reference arrays (needed to ease
> +	 * extension of the BATCH_SUBMIT ioctl). Should be set to
> +	 * sizeof(struct drm_panfrost_bo_ref).
> +	 */
> +	__u32 bo_ref_stride;
> +	__u32 syncobj_ref_stride;
```

Hmm. I'm not /opposed/ and I know kbase uses strides but it seems like
somewhat unwarranted complexity, and there is a combinatoric explosion
here (if jobs, bo refs, and syncobj refs use 3 different versions, as
this encoding permits... as opposed to just specifying a UABI version or
something like that)

```
> +	/**
> +	 * If the submission fails, this encodes the index of the job
> +	 * failed.
> +	 */
> +	__u32 fail_idx;
```

What if multiple jobs fail?

```
> +	/**
> +	 * ID of the queue to submit those jobs to. 0 is the default
> +	 * submit queue and should always exists. If you need a dedicated
> +	 * queue, create it with DRM_IOCTL_PANFROST_CREATE_SUBMITQUEUE.
> +	 */
> +	__u32 queue;
```

s/exists/exist/