Hi Jayesh, thanks, so I should use pci_ioremap_bar() and ioread8() and iowrite8() and the like. What really confused me was the "re" in pci_ioremap_bar() (by the way, there is no API called pci_ioremap(), but only pci_iomap()), suggesting that something different may be done in these two functions apart from better error checking. ________________________________ From: JAYESH TANK [mailto:jayeshece08@gmail.com] Sent: Donnerstag, 27. Juni 2013 10:27 To: Warlich, Christof Cc: kernelnewbies@kernelnewbies.org Subject: Re: pci_iomap() and pci_ioremap_bar() AFAIK, pci_ioremap_bar api provides an error-proof way (relative to pci_ioremap) for PCI memory remap. After the mapping is successful, in case you are writing a portable code, use ioread8 api which provides platform abstraction to the re mapped registers. Hope that helps. BR, Jayesh On Wed, Jun 26, 2013 at 12:42 PM, Warlich, Christof <christof.warlich@siemens.com<mailto:christof.warlich@siemens.com>> wrote: Hi, can anyone explain when I should use void __iomem *regs = pci_iomap(device, barNumber, 0); and when void __iomem *regs = pci_ioremap_bar(device, barNumber); is more appropriate to map PCI memory? Furthermore, after the mapping succeeded, when may I directly access the mapped memory, e.g.: char firstByte = *regs; and when should I better use ioread8() instead?: char firstBype = ioread8(regs); All listed alternatives from above seems to work equally well for me (on x86), so I'm curious to learn what might be the difference. A guess: Does ioread8() work for both memory mapped _and_ IO mapped registers, while the direct access only works for the memory mapped case? Thanks for any clarification. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org<mailto:Kernelnewbies@kernelnewbies.org> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies