On Mon, May 4, 2015 at 3:33 AM, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote: > On 29/04/15 22:18, Luis R. Rodriguez wrote: >> On Tue, Apr 21, 2015 at 1:16 PM, Luis R. Rodriguez >> <mcgrof@xxxxxxxxxxxxxxxx> wrote: >>> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx> >>> >>> This series addresses simple changes to framebuffer drivers to use >>> arch_phys_wc_add() and ioremap_wc() as well as fixing gbefb to add >>> missing mtrr_del() calls. These changes are pretty straight forward. >>> >>> Luis R. Rodriguez (17): >>> video: fbdev: radeonfb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: gbefb: add missing mtrr_del() calls >>> video: fbdev: gbefb: use arch_phys_wc_add() and devm_ioremap_wc() >>> video: fbdev: intelfb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: matrox: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: neofb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: nvidia: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: savagefb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: sisfb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: aty: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: i810: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: pm2fb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: pm3fb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: rivafb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: tdfxfb: use arch_phys_wc_add() and ioremap_wc() >>> video: fbdev: atmel_lcdfb: use ioremap_wc() for framebuffer >>> video: fbdev: geode gxfb: use ioremap_wc() for framebuffer >> >> Hey folks, these are all pretty straight forward, can anyone take them? > > I can take these to fbdev tree. Unfortunately I'm not familiar with x86 > nor mtrr, so I can't really say much about the patches themselves. > I'm on vacation and there's no way I'll be able to usefully review these in the next two weeks. I can describe what's going on in case it helps: On x86 there are two ways to get a write-combining MMIO mapping. The sane way is ioremap_wc, and the ridiculous way is mtrr_add. ioremap_wc does exactly what it appears to do, whereas mtrr_add acts on physical addresses, requires power-of-two alignment, and is unreliable. On all recent hardware, ioremap_wc works, and mtrr_add is problematic on all hardware even if it often works. The silly thing is that mtrr_add pokes at the registers it uses even on hardware with working ioremap_wc. This causes problems (those resources are a very limited resource). The solution I came up with a couple years ago is a new API arch_phys_wc_add. It is a hint that a physical address range should be write-combining. On hardware with working ioremap_wc, it's a no-op. On x86 hardware without working ioremap_wc, it just calls mtrr_add. The upshot is that changing mtrr_add with a WC type to arch_phys_wc_add is OK as long as the driver also uses ioremap_wc or similar _wc APIs. Once everything has been converted, we can unexport mtrr_add, which will have all kinds of benefits. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
