On Sun, Jul 07, 2013 at 10:43:35AM +0800, Jiang Liu wrote: > On 07/04/2013 12:09 AM, Bjorn Helgaas wrote: > > On Wed, Jul 3, 2013 at 9:16 AM, Haicheng Li <haicheng.li@xxxxxxxxxxxxxxx> wrote: > >> With more and more SOCs having pci device integrated into chip (e.g. Intel > >> Atom series), it's useful to add an interface to cleanly hide pci devices from > >> pci device scanning, which is because: > >> > >> 1. phone or tablet OEMs may choose disabling some pci device in the SOC, > >> such as camera ISP in Intel Atom Z2580 chip, and etc. > >> 2. if such disabled devices are not cleanly removed from pci device tree, > >> then pci-core will still try to operate on the relative device control > >> registers while S3 suspend and resume. > >> 3. so hiding such devices from early begining will not only reduce the kernel > >> boot time, but also optimize the latency of system suspend and resume. > > > > Normally the chip provides a way to disable devices by writing a > > configuration register. Then the device doesn't respond when Linux > > enumerates devices, so nothing special is required in the kernel. > > What's different about the Z2580? I'd be surprised if Intel forgot to > > include such a register. Maybe the firmware just isn't smart enough > > to disable the device? If so, it would be better to fix the firmware > > than to add kludges in the kernel. Sorry for slow response due to a travel recently. > Agree, it would be great if chipset and firmware could cooperate to > handle this issue. Otherwise the interface may be abused and causes > trouble to PCI hotplug operations because the notation seg:bus:dev.func > isn't reliable. The PCI bus number may reassigned by OS. I quickly went thru the code and thought the bus # should not be changed in runtime by current code. do you mean after a reboot, the bus# maybe changed with new slot hotplugged? Can you please elabrate this case? hopefully I can enhance the patch to cover it. > > > >> To hide pci devices, just pass such parameters to kernel at boot stage: > >> pci=hide=[<domain>:]<bus>:<slot>.<func>[; ...] -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
