On Mar 14, 2011, at 16:01, Greg KH wrote: > On Mon, Mar 14, 2011 at 02:48:59PM -0500, david.hagood@xxxxxxxxx wrote: >> The problems I've had with rescan happen when the device IS detected on >> the bus, but later has a change of resources - rescan won't reallocate the >> needed resources. >> >> Example #1: An FPGA on the bus that contains a fixed PCIe core, which >> presents an interface on BAR0 allowing the rest of the FPGA to be >> programmed. Once programmed, the FPGA now has BAR0, BAR1, and BAR2. Doing >> a rescan in this case WILL NOT allocate any kernel resources for BAR1 and >> BAR2. >> >> Example #2: A Freescale CPU as a PCIe endpoint. The initial set up as >> defined by the boot code defines BAR0, which gets scanned by the host >> processor on PCI enumeration. Later, the PPC finishes booting its code, >> and reprograms the endpoint, and now BAR1 and BAR2 are defined. Again, >> doing a rescan on the host CPU does NOT reallocate the resources. >> >> And a few months ago, when I asked how to handle this case, I basically >> was told "you are doing it wrong", with no input on how to do it "right". > > There is no "right" way to do this. > > Seriously, other operating systems have thought about doing this, but in > the end, they never shipped a working implementation because it is very > difficult to handle this type of resource change while the system is > running. > > Your only hope is to disconnect the device, and add it back with the new > resources changed. Unless you wish to work on changing the core PCI > code to handle such a change. Those changes might be possible to make, > but as everything works today, it will not. > Do you mean that lower level support for clearing up resources is necessary? Isn't the "pci_remove_bus_device" function clearing up all that a bus scan found and setup for a given device? Does/can this function replace a physical disconnect with proper actual hotplug events (such as expressCard)? I don't understand why the pci_bus_rescan() was able to find a completely new device with BAR0 (we only have one BAR on our device), and set it up, although the BIOS had never seen it. But if I pci_remove_bus_device() it, then rescan again, are you saying that it would re-use a ~profile~ of a past-life device that had only one BAR and reuse that? ... does this only happen if the device was live during BIOS enumeration? I'm still good for my scenario right? Since my FPGA board power up a vegetable, and the BIOS doesn't see it, when I trigger a PCI rescan from userspace, I shouldn't get a half-functionning device with missing resources right? Thanks again for your help, I really made some progress.-- 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
