Ingo Molnar wrote:
* Micha Nelissen <micha@xxxxxxxxxxxxxx> wrote:
Patch is based on earlier patch from Matthew Wilcox.
Hm, there's an awful lot of 'background', 'implementation', 'advantages',
'disadvantages', 'testing' description missing.
Sorry, my bad, wrong assumption that this would be common knowledge.
PCI devices interrupt the CPU using 'legacy' INTx; or PCI-e devices can
do a special write, called an MSI (message signaled interrupt). The
interrupt vector is chosen by the CPU, different devices use different
vectors so that software can keep the interrupt sources separate
(instead of using shared INTx "lines").
Most PCI-e devices support what's called MSI-X, but not all do.
Especially for FPGA based endpoints it's easier to implement only
'regular' MSI support. MSI-X basically involves implementing a lookup
table that maps interrupt types in the device to interrupt vectors for
the CPU. 'Regular' MSI (non MSI-X) only supports a contiguous block of
interrupt vectors: a base vector with a vector count (which is a power
of 2).
The x86 code to allocate these interrupt vectors does not handle the <>
1 vector count case; it would return that it could only handle 1. So
either device drivers had 1 MSI, or the device should support MSI-X to
have multiple interrupts (and handlers) for one device.
This patch adds the needed code to support multiple MSI per device.
Advantages: separate interrupt handlers for separate tasks in the
device. This allows device drivers to be better structured. Easy
'diagnostics' due to /proc/interrupts counting number of interrupts for
separate functionality separately.
Disadvantages: more complex code due to requirement that it is a
contiguous block, so needs some effort to look for a free block with the
requested count.
Tested: on an Atom platform, with a Xilinx based PCI-e core in FPGA.
Please review; thanks,
Micha
--
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
