Re: [PATCH v2 04/13] lpfc: Add push-to-adapter support to sli4

Johannes Thumshirn [off-list ref] writes:

On Wed, Feb 07, 2018 at 10:51:57AM +0100, Johannes Thumshirn wrote:

quoted

quoted

+			/* Enable combined writes for DPP aperture */
+			pg_addr = (unsigned long)(wq->dpp_regaddr) & PAGE_MASK;
+#ifdef CONFIG_X86
+			rc = set_memory_wc(pg_addr, 1);
+			if (rc) {
+				lpfc_printf_log(phba, KERN_ERR, LOG_INIT,
+						"3272 Cannot setup Combined "
+						"Write on WQ[%d] - disable DPP\n",
+						wq->queue_id);
+				phba->cfg_enable_dpp = 0;
+			}
+#else
+			phba->cfg_enable_dpp = 0;
+#endif
+		} else
+			wq->db_regaddr = phba->sli4_hba.WQDBregaddr;

I don't really like the set_memory_wc() call here. Neither do I like the ifdef
CONFIG_X86 special casing.

If you really need write combining, can't you at least use ioremap_wc()?

Coming back to this again (after talking to our ARM/POWER folks internally).
Is this really x86 specific here? I know there are servers with other architectures
using lpfcs out there.

I _think_ write combining should be possible on other architectures (that have
PCIe and aren't dead) as well.

The ioremap_wc() I suggested is probably wrong.

So can you please revisit this? I CCed Mark and Michael, maybe they can help
here.

I'm not much of an I/O guy, but I do know that on powerpc we don't
implement set_memory_wc(). So if you're using that then you do need the
ifdef.

I couldn't easily find the rest of this thread, so I'm not sure if
ioremap_wc() is an option. We do implement that and on modern CPUs at
least it will give you something that's not just a plain uncached
mapping.

cheers