ASPM on the WLAN PCIe bus introduces large latency spikes, which can be
measured with cyclictest:
$ cyclictest --policy=rr --priority=12 --interval=10000 --threads=1 --loops=6000
Disabling ASPM for WLAN reduces the latency spikes from 2,500-3,000 usec
down to 35-65 usec. These latency spikes can impact the user when
real-time processes like Audio (cras) are starved of CPU time, leading
to buffer underruns resulting in crackling/distorted audio.
ASPM is already disabled for Nipperkin devices (CB:63537), so this CL
disables it for both in the shared declaration of
guybrush_czn_dxio_descriptors.
Power impact for Dewatt:
* ASPM enabled
power_VideoCall.FDO_25min_webrtc
w_energy_rate 7.425043688811071
power_Idle.default20min
wh_energy_used 1.4164200000000022
* ASPM disabled
power_VideoCall.FDO_25min_webrtc
w_energy_rate 8.779998551703423
power_Idle.default20min
wh_energy_used 1.4860800000000012
When using Google Meet over WiFi, power increases by ~1.5W.
BUG=b:297970318
TEST=cyclictest --policy=rr --priority=12 --interval=10000 --threads=1 --loops=6000
Change-Id: I16940987d598943bd5d6ace8b4008eba4d4a177c
Signed-off-by: Tim Van Patten <timvp@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77963
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
00864fdba6