Re: [PATCH] RFC drm/i915: Put future HW and their uAPIs under STAGING & BROKEN

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Aug 29, 2019 at 01:17:22PM +0100, Chris Wilson wrote:
> We would like some freedom to break the user API/ABI for future HW but
> yet still expose the driver for upstream development on that HW.
> Currently, we have the i915.force_probe module parameter to avoid binding
> to HW while the driver is under development, but that is still a little
> too soft with respect to the stringent no-regression rules if we also
> plan to be redesigning the uAPI to go along with the new HW.
> 
> To allow the uAPI to be changed during development, only expose that API
> and in development HW under STAGING (and BROKEN). Hopefully, making it
> explicit that such interfaces to that HW are under development and not
> to be blindly enabled by distributions.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> ---
>  drivers/gpu/drm/i915/Kconfig.debug       | 15 +++++++++++++++
>  drivers/gpu/drm/i915/i915_gem.c          | 10 ++++++++++
>  drivers/gpu/drm/i915/intel_device_info.h |  1 +
>  3 files changed, 26 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> index 00786a142ff0..7707d1230b85 100644
> --- a/drivers/gpu/drm/i915/Kconfig.debug
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -36,6 +36,9 @@ config DRM_I915_DEBUG
>  	select DRM_I915_SELFTEST
>  	select DRM_I915_DEBUG_RUNTIME_PM
>  	select DRM_I915_DEBUG_MMIO
> +	select STAGING
> +	select BROKEN
> +	select DRM_I915_DEBUG_EARLY_API

I'm not sure about forcing this all all debug.

>          default n
>          help
>            Choose this option to turn on extra driver debugging that may affect
> @@ -212,3 +215,15 @@ config DRM_I915_DEBUG_RUNTIME_PM
>  	  driver loading, suspend and resume operations.
>  
>  	  If in doubt, say "N"
> +
> +config DRM_I915_DEBUG_EARLY_API
> +	bool "Expose new HW uAPIs for early testing"
> +	depends on DRM_I915
> +	depends on STAGING
> +	depends on BROKEN

instead why not
select STAGING
select BROKEN
depends on DRM_I915_DEBUG

?

> +	default n
> +	help
> +	  Expose in-development uAPI for early testing on HW. Such uAPI
> +	  will likely subtly change before release and must not be relied upon.
> +
> +	  If in doubt, say "N"
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index bb39c64a0a17..eab2219d7a50 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1344,6 +1344,15 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
>  {
>  	int ret;
>  
> +	if (INTEL_INFO(dev_priv)->early_render_uapi) {
> +		if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_EARLY_API)) {
> +			ret = -EIO;
> +			goto err_disable;
> +		}
> +
> +		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
> +	}
> +
>  	/* We need to fallback to 4K pages if host doesn't support huge gtt. */
>  	if (intel_vgpu_active(dev_priv) && !intel_vgpu_has_huge_gtt(dev_priv))
>  		mkwrite_device_info(dev_priv)->page_sizes =
> @@ -1476,6 +1485,7 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
>  		intel_timelines_fini(dev_priv);
>  	}
>  
> +err_disable:
>  	if (ret == -EIO) {
>  		/*
>  		 * Allow engines or uC initialisation to fail by marking the GPU
> diff --git a/drivers/gpu/drm/i915/intel_device_info.h b/drivers/gpu/drm/i915/intel_device_info.h
> index 92e0c2e0954c..5931f619e66b 100644
> --- a/drivers/gpu/drm/i915/intel_device_info.h
> +++ b/drivers/gpu/drm/i915/intel_device_info.h
> @@ -107,6 +107,7 @@ enum intel_ppgtt_type {
>  	func(is_mobile); \
>  	func(is_lp); \
>  	func(require_force_probe); \
> +	func(early_render_uapi); \
>  	/* Keep has_* in alphabetical order */ \
>  	func(has_64bit_reloc); \
>  	func(gpu_reset_clobbers_display); \
> -- 
> 2.23.0
> 
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