[Intel-gfx] [PATCH 2/2] drm/i915: Add ring_mask module parameter

[Chris Wilson]

Quoting Stuart Summers (2019-08-28 00:14:35)
> Add a new module parameter, ring_mask, to allow for disabling
> engines during i915 load. This mask follows the intel_engine_id
> enum and can be used to hide specified engines from i915 and
> from userspace.
> 
> Signed-off-by: Stuart Summers <stuart.summers at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_params.c       | 3 +++
>  drivers/gpu/drm/i915/i915_params.h       | 3 ++-
>  drivers/gpu/drm/i915/intel_device_info.c | 6 ++++++
>  3 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 296452f9efe4..6a17fe6ea3a2 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -178,6 +178,9 @@ i915_param_named(enable_gvt, bool, 0400,
>         "Enable support for Intel GVT-g graphics virtualization host support(default:false)");
>  #endif
>  
> +i915_param_named_unsafe(ring_mask, uint, 0400,
> +       "Mask of engine rings to enable. (default: all supported engines enabled)");
> +
>  static __always_inline void _print_param(struct drm_printer *p,
>                                          const char *name,
>                                          const char *type,
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index d29ade3b7de6..d803bf5faac4 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -77,7 +77,8 @@ struct drm_printer;
>         param(bool, verbose_state_checks, true) \
>         param(bool, nuclear_pageflip, false) \
>         param(bool, enable_dp_mst, true) \
> -       param(bool, enable_gvt, false)
> +       param(bool, enable_gvt, false) \
> +       param(unsigned int, ring_mask, (unsigned int)-1)
>  
>  #define MEMBER(T, member, ...) T member;
>  struct i915_params {
> diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
> index caef01b1da23..f833280f2ef6 100644
> --- a/drivers/gpu/drm/i915/intel_device_info.c
> +++ b/drivers/gpu/drm/i915/intel_device_info.c
> @@ -993,10 +993,16 @@ void intel_device_info_init_mmio(struct drm_i915_private *dev_priv)
>         u32 media_fuse;
>         u16 vdbox_mask;
>         u16 vebox_mask;
> +       u32 orig_engine_mask = info->engine_mask;
>  
>         if (INTEL_GEN(dev_priv) < 11)
>                 return;
>  
> +       info->engine_mask &= i915_modparams.ring_mask;

The challenge is we can't use our engine_mask for this as that is an
internal bitfield that may change overtime -- and we definitely don't
want the modparam to disable different engines on different kernel
releases.

> +       if (info->engine_mask != orig_engine_mask)
> +               DRM_WARN("loading with reduced engine mask 0x%x\n",
> +                        info->engine_mask);

It's operating under direct control from the user, so dev_notice (as we
treat it as a quirk).
-Chris