Messages in this thread Patch in this message | | | Date | Fri, 27 Jun 2008 13:17:24 +0100 | From | David Vrabel <> | Subject | Re: PCI: MSI interrupts masked using prohibited method |
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Jesse Barnes wrote: > On Tuesday, June 24, 2008 3:46 am David Vrabel wrote: >> PCI MSI interrupts are masked and unmasked using a method (by writing >> the MSI Enable capability bit) that is prohibited by the PCI specification. > > Yeah, it's probably quite a bit slower too (I assume you're talking about > io_apic_64's msi_mask_irq). Seems like masking this at the ioapic level > would make more sense anyway... > >> This behaviour can cause missed interrupts with some devices if the >> interrupt is asserted by the hardware while MSI is disabled. >> >> I believe the interrupt should be masked/unmasked on the interrupt >> controller (the APIC on x86, for example). I'm going to test this now >> and see if it works.
After further research it seems that MSI interrupts aren't routed via the IO-APIC, so this cannot be done.
I think the only solution is to not perform any sort of masking and rely on the device driver being able to handle this.
David -- David Vrabel, Senior Software Engineer, Drivers CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562 Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/ PCI: don't mask MSI's with MSI Enable bit
The PCI Local Bus Specification Revision 3.0, section 6.8.1.3. Message Control for MSI on page 236, prohibited the use of the MSI Enable bit for masking and unmasking the interrupt.
"MSI Enable: If 1 and the MSI-X Enable bit in the MSI-X Message Control register (see Section 6.8.2.3) is 0, the function is permitted to use MSI to request service and is prohibited from using its INTx# pin (if implemented; see Section 6.2.4 Interrupt pin register). System configuration software sets this bit to enable MSI. A device driver is prohibited from writing this bit to mask a function’s service request."
There is no alternative method for mask/unmask on PCI devices with MSI and no specific mask bit. In this case, the device driver will have to ensure (via some hardware specific mechanism) that MSI's are only generated when the device driver can handle them.
Signed-off-by: David Vrabel <david.vrabel@csr.com> --- drivers/pci/msi.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
Index: linux-2.6-working/drivers/pci/msi.c =================================================================== --- linux-2.6-working.orig/drivers/pci/msi.c 2008-06-27 12:24:17.000000000 +0100 +++ linux-2.6-working/drivers/pci/msi.c 2008-06-27 12:25:05.000000000 +0100 @@ -141,7 +141,18 @@ mask_bits |= flag & mask; pci_write_config_dword(entry->dev, pos, mask_bits); } else { - msi_set_enable(entry->dev, !flag); + /* + * If there is no mask bit, this irq cannot be + * masked and the driver will have to use + * whatever hardware specific mechanisms are + * available to control the sending of MSI + * messages. + * + * Note: cannot attempt to mask via the MSI + * enable bit as that is prohibited by the PCI + * specification. + */ + return; } break; case PCI_CAP_ID_MSIX: | |