On Tue, 2014-09-30 at 09:04 -0600, Bjorn Helgaas wrote: > On Mon, Sep 29, 2014 at 9:40 PM, Benjamin Herrenschmidt > <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > Hi folks ! (Adding linux-pci and Yijing, which I stupidly forgot) > > Some ATM devices have a limitation in the number of address bits they > > can generate for MSI and MSI-X (similar to their DMA limitations). > > > > This makes it impossible to "reach" the MSI regions for 64-bit MSI on > > our POWER server chips since those must have some of the top address > > bits set. > > > > For DMA today, we have the DMA mask that handles that limitation fine > > at the arch level. > > > > However we have nothing for MSIs. > > > > So far, we've workaround it with a kludge. We maintain a powerpc > > specific flag in some auxilliary data structure that we keep along > > with PCI devices and we have a quirk in arch/powerpc/kernel/pci_64.c > > that will set that flag for some known devices. > > > > At this point we have only added two known ATI IDs corresponding to > > radeons we ship with our machines, but as you can imagine, that not > > a very good long term solution. > > > > Ideally we want that quirk to be set by the driver. The radeon driver > > "knows" what the addressing capacity of the device it. > > > > So the easiest way to handle that for me would be to move that flag > > "force_32bit_msi" from our arch data structure to pci_dev, and have > > the radeon driver set it before it enables MSIs. > > > > However that would have the side effect of also limiting other archs > > to 32-bit MSIs while the 40-bit of address (or so ....) that the radeon > > supports might be sufficient for 64-bit MSIs to work on these. > > > > The slightly fancier approach would be to have something like an > > msi64_set_address_mask() where the driver can configure the supported > > mask for 64-bit MSIs. > > > > This would allow the architecture code to make a smarter decision based > > on what is actually possible. > > > > Any preference, comment or suggestion ? > > Please CC: linux-pci and Yijing Wang <wangyijing@xxxxxxxxxx> unless > there's something secret here. I didn't add them myself in case you > think this is sensitive. > > If I understand correctly, per spec, devices can support MSI with > either 32-bit or 64-bit addresses, and they advertise their capability > via the "64 bit address capable" bit in the Message Control register. > And per spec, devices that support MSI-X must support 64-bit > addresses. > > So apparently these devices are not spec compliant. I suggest that > you move the "force_32bit" flag into struct pci_dev, set it via a > quirk, and change drivers/pci/msi.c to use it to override the > "msi_attrib.is_64" settings in msi_setup_entry() and/or > msix_setup_entries(). > > At this point, I don't see value in adding the complexity to support > intermediate address sizes between 32 and 64 bits. Ok, I tend to agree. Cheers, Ben. -- 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
