[Xen-devel] CPUIDLE: enable MSI capable HPET for timer broadcast

["Wei, Gang" <gang.wei@xxxxxxxxx>]

The HPET broadcast was default not enabled because the old code use HPET 
channel 0 in legacy replacing mode which will hide both PIT & RTC irqs and 
cause issues if RTC is needed in some cases. The upstream default broadcast 
timer is PIT, which is in periodic mode (100HZ) and would be expensive to be 
used as oneshot. MSI capable HPET is coming into being. It is capable to 
deliver interrupt through FSB directly, and has no side effect.

This patch extends support for MSI HPET based on original legacy HPET code. The 
broadcast timer selection logic becomes: 1. if MSI capable HPET available, use 
multiple HPET channels (no more than possible cpu num) in MSI mode; 2. else if 
legacy replacing mode available for HPET & 'hpetbroadcast' option is given in 
cmd line, use HPET channel 0 in legacy mode; 3 else use PIT.

While entering broadcast, it gets a hpet channel (look for a spare one first, 
if failing allocate a shared one), attach to current cpu, setup the irq 
affinity & broadcast cpumask. While exiting broadcast, it detach the used hpet 
channel and try to change the owner if the broadcast mask is not empty. Some 
optimizations(static affinity) were done for (MSI HPET channels >= possible cpu 
num) case.

A new hw_interrupt_controller 'HPET_MSI' is created for HPET MSI interrupt 
handling.

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

Attachment: hpet-msi-20090320.patch
Description: hpet-msi-20090320.patch

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