mb/google/guybrush: Disable WLAN ASPM

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>

src/mainboard/google/guybrush/port_descriptors.c

@@ -18,8 +18,8 @@ static fsp_dxio_descriptor guybrush_czn_dxio_descriptors[] = {
 		.device_number = PCI_SLOT(WLAN_DEVFN),
 		.function_number = PCI_FUNC(WLAN_DEVFN),
 		.link_aspm = ASPM_L1,
-		.link_aspm_L1_1 = true,
+		.link_aspm_L1_1 = false,
-		.link_aspm_L1_2 = true,
+		.link_aspm_L1_2 = false,
 		.turn_off_unused_lanes = true,
 		.clk_req = CLK_REQ0,
 		.port_params = {PP_PSPP_AC, 0x133, PP_PSPP_DC, 0x122}

src/mainboard/google/guybrush/variants/nipperkin/variant.c

@@ -1,13 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include <baseboard/variants.h>
-#include <string.h>
 
 void variant_update_dxio_descriptors(fsp_dxio_descriptor *dxio_descriptors)
 {
-	dxio_descriptors[WLAN].link_aspm_L1_1 = false;
-	dxio_descriptors[WLAN].link_aspm_L1_2 = false;
-
 	/* Fix link speed to GEN2 - b/228830362 */
 	dxio_descriptors[WLAN].link_speed_capability = GEN2;
 	dxio_descriptors[WLAN].port_params[0] = PP_PSPP_AC;