Re: [PATCH] cxl: Set the valid bit in PE for dedicated mode

Hi Mpe,

Thanks for reviewing the patch

Michael Ellerman [off-list ref] writes:

quoted

+	ctx->elem->software_state = cpu_to_be32(CXL_PE_SOFTWARE_STATE_V);
+	/* Make sure the changes to the PE are visible to the card */

A barrier orders something vs something else. So what's the something
else in this case? Is it the afu_reset() below, what does that actually do?

The issue is with call to afu_enable() after the call to afu_reset that
would start the AFU. If this load gets reordered and PSL doesnt see the
valid bit set for this structure then it will result in PSL entering a
freeze-state.

Though on second thoughts afu_enable() is grabbing a spin-lock before
doing an mmio to start the AFU that would be forcing a barrier
anyways. But since that spans the function boundary hence to be safe
have added a write barrier after populating the process element.

Lastly function is not performance critical as it will be usually called
in the life time of a process only once. So the impact smp_wmb() is
having would be minimal.

-- 
Vaibhav Jain [off-list ref]
Linux Technology Center, IBM India Pvt. Ltd.