Hi,
On Mon, 2022-03-21 at 13:12 +0000, Tvrtko Ursulin wrote:
On 21/03/2022 12:33, Thomas Hellström wrote:
On Mon, 2022-03-21 at 12:22 +0000, Tvrtko Ursulin wrote:
On 21/03/2022 11:03, Thomas Hellström wrote:
Hi, Tvrtko.
On 3/21/22 11:27, Tvrtko Ursulin wrote:
On 19/03/2022 19:42, Michael Cheng wrote:
To align with the discussion in [1][2], this patch series drops all usage of wbvind_on_all_cpus within i915 by either replacing the call with certain drm clflush helpers, or reverting to a previous logic.
AFAIU, complaint from [1] was that it is wrong to provide non x86 implementations under the wbinvd_on_all_cpus name. Instead an arch agnostic helper which achieves the same effect could be created. Does Arm have such concept?
I also understand Linus' email like we shouldn't leak incoherent IO to other architectures, meaning any remaining wbinvd()s should be X86 only.
The last part is completely obvious since it is a x86 instruction name.
Yeah, I meant the function implementing wbinvd() semantics.
But I think we can't pick a solution until we know how the concept maps to Arm and that will also include seeing how the drm_clflush_sg for Arm would look. Is there a range based solution, or just a big hammer there. If the latter, then it is no good to churn all these reverts but instead an arch agnostic wrapper, with a generic name, would be the way to go.
But my impression was that ARM would not need the range-based interface either, because ARM is only for discrete and with discrete we're always coherent.
Not sure what you mean here - what about flushing system memory objects on discrete? Those still need flushing on paths like suspend which this series touches. Am I missing something?
System bos on discrete should always have
I915_BO_CACHE_COHERENT_FOR_READ | I915_BO_CACHE_COHERENT_FOR_WRITE
either by the gpu being fully cache coherent (or us mapping system write-combined). Hence no need for cache clflushes or wbinvd() for incoherent IO.
That's adhering to Linus'
"And I sincerely hope to the gods that no cache-incoherent i915 mess ever makes it out of the x86 world. Incoherent IO was always a historical mistake and should never ever happen again, so we should not spread that horrific pattern around."
/Thomas