On Mon, Mar 20, 2017 at 04:26:27PM +0000, Lorenzo Pieralisi wrote: > On Mon, Mar 20, 2017 at 11:06:36AM -0500, Bjorn Helgaas wrote: > > [...] > > > > > > @@ -3375,7 +3375,7 @@ int pci_remap_iospace(const struct resource *res, phys_addr_t phys_addr) > > > > > return -EINVAL; > > > > > > > > > > return ioremap_page_range(vaddr, vaddr + resource_size(res), phys_addr, > > > > > - pgprot_device(PAGE_KERNEL)); > > > > > + pgprot_noncached(PAGE_KERNEL)); > > > > > > > > ... > > > > I do find this puzzling because I naively expected pgprot_noncached() > > > > to match up with ioremap_nocache(), and apparently it doesn't. > > > > > > > > For example, ARM64 ioremap_nocache() uses PROT_DEVICE_nGnRE, which > > > > doesn't match the MT_DEVICE_nGnRnE in pgprot_noncached(). > > > > > > > > The point of these patches is to use non-posted mappings. Apparently > > > > you can do that with pgprot_noncached() here, but ioremap_nocache() > > > > isn't enough for the config space mappings? > > > > > > This is for iospace it seems, so the other patch I think was for > > > config space. > > > > I understand that 02/20 is for PCI I/O port space and 03/20 is for PCI > > config space. I'm confused because I thought we wanted the same > > non-posted mapping for both, but looks like they're different. > > > > Patch 02/20 uses ioremap_page_range(..., pgprot_noncached(PAGE_KERNEL)) > > to map PCI I/O port space: > > > > #define pgprot_noncached(prot) \ > > __pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_nGnRnE) | PTE_PXN | PTE_UXN) > > > > Patch 03/20 uses ioremap_nocache() to map PCI config space: > > > > #define ioremap_nocache(addr, size) __ioremap((addr), (size), __pgprot(PROT_DEVICE_nGnRE)) > > > > So the I/O port mapping uses MT_DEVICE_nGnRnE, while the config space > > mapping uses PROT_DEVICE_nGnRE, which looks different. > > On ARM64 (PATCH 4) and ARM (PATCH 5) we override pci_remap_cfgspace() > with implementations that provide non-posted writes bus attributes, > PATCH 3 is just there to provide a "safe" (well, I need input on that) > fall-back. Ah, thanks, that makes sense to me finally! After patch 4, pci_remap_cfgspace() uses PROT_DEVICE_nGnRnE, which does look like the MT_DEVICE_nGnRnE used in the ioremap_page_range() path. I wonder if we can get rid of pgprot_device() altogether? Patch 2 removed the use in pci_remap_iospace(), and patch 18 removes the use in tegra_pcie_bus_alloc(). Bjorn
