Re: ((struct pci_dev*)dev)->resource[...].start

[Jeff Garzik <jgarzik@mandrakesoft.com>]

"Khachaturov, Vassilii" wrote:
> Can someone please confirm if my assumptions below are correct:
> 1) Unless someone specifically tampered with my driver's device since the OS
> bootup, the mapping of the PCI base address registers to virtual memory will
> remain the same (just as seen in /proc/pci, and as reflected in <subj>)? If
> not, is there a way to freeze it for the time I want to access it?

This is not a safe assumption, because the OS may reprogram the PCI BARs
at certain times.  The rule is:  ALWAYS read from dev->resource[] unless
you are a bus driver (PCI bridges, for example, need to assign
resources).

Further, access to PCI BARs -and- dev->resource[] in a driver is wrong
until you have called pci_enable_device.  Resource and IRQ assignment
potentially occurs at pci_enable_device time, so BAR is [potentially]
undefined before then.

Finally, make sure to use pci_resource_{start,end,len,flags} macros to
make your core more portable and future-proof.

> 2) (Basically, the question is "Do I understand Documentation/IO-mapping.txt
> right?")
> PCI memory, whenever IO type or memory type, can not be dereferenced but
> should be accessed with readb() etc. On i386, PCI mem (memory type) can be
> accessed by direct pointer access, but this is not portable.

We will yell at you mightily if you directly access PCI mem with a
pointer.  As you say it only works on i386 -- but IIRC since ioremap is
required, we are perfectly free to change or modify that assumption. 
For example ioremap might [have to] care about whether or not a pci mem
region is prefetchable.

-- 
Jeff Garzik      | Game called on account of naked chick
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