Hi jfs, Thanks for info. I have seen a machine, in which BIOS was having a option like :- map BAR above 4GB/2GB/2.5GB... such 3 or 4 options. Using such option, it was mapping BAR above the specified range. Now, not all machines are having such options. So, i was just trying to explore a way, to get BAR mapped above some range. On Wed, Oct 1, 2008 at 6:49 PM, jean-francois simon <jfsthemis@xxxxxxxxx> wrote: > yogeshwar sonawane wrote: >> Hi all, >> >> By reading the PCI BAR value from PCI config space, one gets BAR >> region starting address for that PCI device. >> If device is 32-bit capable, then max 6 BARs are possible, but for >> 64-bit PCI card, only 3 BAR regions are possible. > > ok. > >> >> Generally, BIOS sets the address/value in these BARs which device >> driver reads & access the device. I am referring linux OS. >> So the BAR region address range OR starting address assignment is done by BIOS. >> Can we change this address through device driver, by writing the PCI >> BARs in PCI config space ? >> There are apis to read/write to PCI config space. > > i don't think this is possible for a driver to reassign pci resources. >> >> Can i map a BAR region of a PCI device, above 4 GB (i.e. 64-bit addr) >> instead of 32bit address(higher 32bits as 0) ? >> If possible, how to do this ? > > check your bios: AMI bioses can work with PCI 64b devices. but i don't > know if linux can be forced to assign 64b pci devices above 4GB. >> >> Writing/changing BAR register value through device driver, will >> propagate till PCI root controller ? >> Can setpci command be used for this ? > > i dont think you want to do that. the pci enumeration is the > responsibility of the kernel, and you can't change this from a driver. > look at /proc/iomem and you will see your device is part of a pci bus > within a given MMIO window. maybe you can change yr device BARs within > that window...but even this i dont recommend. > > the kernel parameter "pci=assign-busses" is supposed to re-enumerate the > PCI hierarchy and you may like what linux did in that area better than > what the bios did. > > i am saying all this with a grain of salt. i am also wondering how pci > enumeration/resource allocation really works....i have recently looked > at the code and it is not easy to figure out if on an arch like x86_64, > devices can be set > 4GB, if and when they are moved... > but i'll look more and get back to you if i find anything > -jfs > > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
