[Intel-gfx] [PATCH 1/1] drm/i915: Disable pread/pwrite ioctl's for future platforms (v2)

[Dixit, Ashutosh]

On Thu, 11 Mar 2021 12:20:17 -0800, Jason Ekstrand wrote:
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index b2e3b5cfccb4a..78ad5a9dd4784 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -374,10 +374,19 @@ int
>  i915_gem_pread_ioctl(struct drm_device *dev, void *data,
>		     struct drm_file *file)
>  {
> +	struct drm_i915_private *i915 = to_i915(dev);
>	struct drm_i915_gem_pread *args = data;
>	struct drm_i915_gem_object *obj;
>	int ret;
>
> +	/* Pread is disallowed for all platforms after TGL-LP */
> +	if (INTEL_GEN(i915) >= 12 && !IS_TIGERLAKE(i915))
> +		return -EOPNOTSUPP;
> +
> +	/* All discrete memory platforms are Gen12 or above */
> +	if (WARN_ON(HAS_LMEM(i915)))
> +		return -EOPNOTSUPP;

Not sure but you are probably trying to make it explicit that pread/pwrite
are truly gone on dGfx? Because real dGfx are Gen12+ the code will return
from the first if statement and never get to the second if statement. And
there's talk on the relocation thread about tripping fake LMEM here for
platforms prior to Gen12.

So I'd suggest get rid of this second if statement and only retain the
first (for both pread and pwrite) since that seems to be entirely
sufficient.