Re: [PATCH v6 16/25] drm/i915: Update execlists context descriptor format commentary

Tvrtko Ursulin
2016-04-27T13:22:52Z

On 26/04/16 21:06, Chris Wilson wrote:
> The comments describing the Context Descriptor Format are off by a bit
> for the size of the context ID.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Dave Gordon <david.s.gordon@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
> drivers/gpu/drm/i915/intel_lrc.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index b5c2c1931a5f..5d8ee9059eee 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -305,10 +305,11 @@ logical_ring_init_platform_invariants(struct intel_engine_cs *engine)
> * which remains valid until the context is unpinned.
> *
> * This is what a descriptor looks like, from LSB to MSB:
> - * bits 0-11: flags, GEN8_CTX_* (cached in ctx_desc_template)
> + * bits 0-11: flags, GEN8_CTX_* (cached in ctx_desc_template)
> * bits 12-31: LRCA, GTT address of (the HWSP of) this context
> - * bits 32-51: ctx ID, a globally unique tag (the LRCA again!)
> - * bits 52-63: reserved, may encode the engine ID (for GuC)
> + * bits 32-52: ctx ID, a globally unique tag (the LRCA again!)
> + * bits 53-54: mbz, reserved for use by hardware
> + * bits 55-63: group ID, currently unused and set to 0
> */
> static void
> intel_lr_context_descriptor_update(struct intel_context *ctx,
> @@ -319,9 +320,9 @@ intel_lr_context_descriptor_update(struct intel_context *ctx,
> lrca = ctx->engine[engine->id].lrc_vma->node.start +
> LRC_PPHWSP_PN * PAGE_SIZE;
>
> - desc = engine->ctx_desc_template; /* bits 0-11 */
> + desc = engine->ctx_desc_template; /* bits 0-11 */
> desc |= lrca; /* bits 12-31 */
> - desc |= (lrca >> PAGE_SHIFT) << GEN8_CTX_ID_SHIFT; /* bits 32-51 */
> + desc |= (lrca >> PAGE_SHIFT) << GEN8_CTX_ID_SHIFT; /* bits 32-52 */
>
> ctx->engine[engine->id].lrc_desc = desc;
> }
>

Verified against the docs and it is correct.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko