From mboxrd@z Thu Jan 1 00:00:00 1970 From: lorenzo.pieralisi@arm.com (Lorenzo Pieralisi) Date: Thu, 9 Feb 2017 14:38:05 +0000 Subject: [QUESTION] Early Write Acknowledge for PCIe configuration space In-Reply-To: References: <6092525.UgRCY3dpzP@wuerfel> <20170106114231.GC15333@arm.com> <20170208183530.GA27720@red-moon> Message-ID: <20170209143805.GA31693@red-moon> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Feb 09, 2017 at 11:42:18AM +0000, Gabriele Paoloni wrote: [...] > > > The ARMv8 ARM also says that the E attribute is a hint, so there's no > > > guarantee that it's actually honoured by the implementation. However, > > > now that it explicitly mentions PCI config space, the intention is > > clearly > > > that nE *is* honoured for systems using PCIe, so I agree that we > > should make > > > this change. I don't want to use the nE type for all ioremap > > invocations, > > > though. > > > > I suspect this is a potential issue on ARM 32-bit systems too(?). > > Fixing > > IO space should be reasonably simple, we just have to change the > > pgprot_device() in pci_remap_iospace() to pgprot_noncached() (they are > > the same attributes on ARM 32-bit already if I am not mistaken). > > Agreed on this. Actually I noticed that pci_remap_iospace() is __weak > but no other definitions are present... Yes I will remove it. > > What do we want to do for config space ? Implement ioremap_uc() for > > ARM/ARM64 (and add a devm_ioremap_uc() call to use it in basically all > > drivers/pci/host implementations to map config space - or we just patch > > the ioremap calls in drivers/pci/ecam.c and we assume the other hosts > > controllers have purportedly called devm_ioremap() because on those > > platforms it just works ok till further notice ?) > > Well if my understanding is correct we are 100% positive that this issue > affects controllers mounted on ARM and ARM64, right? > If this is correct I would look at drivers/pci/host/Kconfig and see which > controllers depend on ARM or ARM64; for these controllers I would replace > devm_ioremap() with devm_ioremap_uc(). > Obviously I would also replace the calls in drivers/pci/ecam.c... > > What do you think? I share Will's concern on the _uc API, I will probably add a pci_remap_cfgspace() API that would fall back to ioremap_nocache() by default (ie if the arch does not override it). Adding a devm_ioremap_* version seems overkill to me. I will send a patch series, we will take it from there. Cheers, Lorenzo