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

[Michael Ellerman]

Johannes Thumshirn <jthumshirn at suse.de> writes:

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