On Wed, Apr 22, 2015 at 8:23 AM, Luis R. Rodriguez <mcgrof@xxxxxxxx> wrote: > On Tue, Apr 21, 2015 at 11:39:39PM -0600, Jason Gunthorpe wrote: >> On Wed, Apr 22, 2015 at 01:39:07AM +0200, Luis R. Rodriguez wrote: >> > > Mike, do you think the time is right to just remove the iPath driver? >> > >> > With PAT now being default the driver effectively won't work >> > with write-combining on modern kernels. Even if systems are old >> > they likely had PAT support, when upgrading kernels PAT will work >> > but write-combing won't on ipath. >> >> Sorry, do you mean the driver already doesn't get WC? Or do you mean >> after some more pending patches are applied? > > No, you have to consider the system used and the effects of calls used > on the driver in light of this table: > > ---------------------------------------------------------------------- > MTRR Non-PAT PAT Linux ioremap value Effective memory type > ---------------------------------------------------------------------- > Non-PAT | PAT > PAT > |PCD > ||PWT > ||| > WC 000 WB _PAGE_CACHE_MODE_WB WC | WC > WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC > WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | UC > WC 011 UC _PAGE_CACHE_MODE_UC UC | UC > ---------------------------------------------------------------------- > > (*) denotes implementation defined and is discouraged > > ioremap_nocache() will use _PAGE_CACHE_MODE_UC_MINUS by default today, > in the future we want to flip the switch and make _PAGE_CACHE_MODE_UC > the default. When that flip occurs it will mean ipath cannot get > write-combining on both non-PAT and PAT systems. Now that is for > the future, lets review the current situation for ipath. > > For PAT capable systems if mtrr_add() is used today on a Linux system on a > region mapped with ioremap_nocache() that will mean you effectively nullify the > mtrr_add() effect as the combinatorial effect above yields an effective memory > type of UC. Are you sure? I thought that ioremap_nocache currently is UC-, so mtrr_add + ioremap_nocache gets WC even on PAT systems. Going forward, when mtrr_add is gone, this will change, of course. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
