pci_iomap() and pci_ioremap_bar()

Warlich, Christof christof.warlich at siemens.com
Fri Jun 28 03:17:39 EDT 2013

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 at gmail.com]
Sent: Donnerstag, 27. Juni 2013 10:27
To: Warlich, Christof
Cc: kernelnewbies at 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.


On Wed, Jun 26, 2013 at 12:42 PM, Warlich, Christof <christof.warlich at siemens.com<mailto:christof.warlich at siemens.com>> wrote:

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.

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