1. ASPM概述
PCIe总线的电源管理包含ASPM(Active State Power Management)和软件电源管理两方面内容。所谓的ASPM是指PCIe链路在没有系统软件参与的情况下，由PCIe链路自发进行的电源管理方式。如下是PCIe的ASPM的状态机，其L1是强制性的规定，而L0s是可选的。
2. Debugging
2.1 如何查看ASPM的状态
对于Linux系统来说，可以使用“lspci -vvv”指令来查看ASPM的状态。
2.1.1 When ASPM is enabled
如下是一个PCIe ASPM使能的示例，请参考：
05:00.0 Network controller: Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express) (rev 01)
Subsystem: Atheros Communications Inc. Device 3099
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0, Cache Line Size: 64 bytes
Interrupt: pin A routed to IRQ 19
Region 0: Memory at dbdf0000 (64-bit, non-prefetchable) [size=64K]
Capabilities: [40] Power Management version 2
Flags: PMEClk- DSI- D1+ D2- AuxCurrent=375mA PME(D0+,D1+,D2-,D3hot+,D3cold-)
Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit-
Address: 00000000 Data: 0000
Capabilities: [60] Express (v1) Legacy Endpoint, MSI 00
DevCap: MaxPayload 128 bytes, PhantFunc 0, Latency L0s <512ns, L1 <64us
ExtTag- AttnBtn- AttnInd- PwrInd- RBE- FLReset-
DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop-
MaxPayload 128 bytes, MaxReadReq 512 bytes
DevSta: CorrErr- UncorrErr+ FatalErr- UnsuppReq+ AuxPwr- TransPend-
LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM unknown, Latency L0 <512ns, L1 <64us
ClockPM- Surprise- LLActRep- BwNot-
LnkCtl: ASPM L1 Enabled; RCB 128 bytes Disabled- Retrain- CommClk+
ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
Capabilities: [90] MSI-X: Enable- Count=1 Masked-
Vector table: BAR=0 offset=00000000
PBA: BAR=0 offset=00000000
Capabilities: [100] Advanced Error Reporting
UESta: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq+ ACSViol-
UEMsk: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
UESvrt: DLP+ SDES- TLP- FCP+ CmpltTO- CmpltAbrt- UnxCmplt- RxOF+ MalfTLP+ ECRC- UnsupReq- ACSViol-
CESta: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
CEMsk: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
AERCap: First Error Pointer: 14, GenCap+ CGenEn- ChkCap+ ChkEn-
Capabilities: [140] Virtual Channel <?>
Capabilities: [160] Device Serial Number 00-00-00-00-00-00-00-00
Kernel driver in use: ath9k
Kernel modules: ath9k2.1.2 When ASPM is disabled
如下是一个PCIe ASPM没有使能的示例，请参考：
localhost ~ # lspci -vvvv -s 03:00
03:00.0 Network controller: Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express) (rev 01)
Subsystem: Atheros Communications Inc. Device 309a
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0, Cache Line Size: 64 bytes
Interrupt: pin A routed to IRQ 17
Region 0: Memory at f0100000 (64-bit, non-prefetchable) [size=64K]
Capabilities: [40] Power Management version 2
Flags: PMEClk- DSI- D1+ D2- AuxCurrent=375mA PME(D0+,D1+,D2-,D3hot+,D3cold-)
Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit-
Address: 00000000 Data: 0000
Capabilities: [60] Express (v1) Legacy Endpoint, MSI 00
DevCap: MaxPayload 128 bytes, PhantFunc 0, Latency L0s <512ns, L1 <64us
ExtTag- AttnBtn- AttnInd- PwrInd- RBE- FLReset-
DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop-
MaxPayload 128 bytes, MaxReadReq 512 bytes
DevSta: CorrErr- UncorrErr+ FatalErr- UnsuppReq+ AuxPwr- TransPend-
LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM unknown, Latency L0 <512ns, L1 <64us
ClockPM- Surprise- LLActRep- BwNot-
LnkCtl: ASPM Disabled; RCB 128 bytes Disabled- Retrain- CommClk+
ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
Capabilities: [90] MSI-X: Enable- Count=1 Masked-
Vector table: BAR=0 offset=00000000
PBA: BAR=0 offset=00000000
Capabilities: [100] Advanced Error Reporting
UESta: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq+ ACSViol-
UEMsk: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
UESvrt: DLP+ SDES- TLP- FCP+ CmpltTO- CmpltAbrt- UnxCmplt- RxOF+ MalfTLP+ ECRC- UnsupReq- ACSViol-
CESta: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
CEMsk: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
AERCap: First Error Pointer: 14, GenCap+ CGenEn- ChkCap+ ChkEn-
Capabilities: [140] Virtual Channel <?>
Capabilities: [160] Device Serial Number 00-00-00-00-00-00-00-00
Kernel driver in use: ath9k
Kernel modules: ath9k2.1.3 为什么我的设备ASPM没有使能？
ASPM应该由RC和所有EP自动协商。如果你的设备查询之后，发现禁用了ASPM，可能有以下原因：
- BIOS没有使能ASPM的相关设置
- L0s是可选的，可能你得设备只支持L1
- BIOS可能发生了相关未知的问题
- ASPM不仅需要EP的支持，也需要RC的支持
2.2 如何使能ASPM
当前我们大多数的Wi-Fi芯片所使用的接口都是PCIe，而且大多数都是手持设备，所以这时候对于设备的功耗就有很大的要求。所以也就需要支持ASPM的L0s状态，以达到最佳的功耗状态。
2.2.1 如何在Kernel中使能ASPM
操作系统一般不干涉ASPM，但是我们可以通过Kernel来调试PCIe RC/EP的ASPM设置。所以Kernel一般需要使能CONFIG_PCIEASPM配置，以此达到能够调试的目的：
config PCIEASPM
bool "PCI Express ASPM support(Experimental)"
depends on PCI && EXPERIMENTAL && PCIEPORTBUS
default n
help
This enables PCI Express ASPM (Active State Power Management) and
Clock Power Management. ASPM supports state L0/L0s/L1.
When in doubt, say N.2.2.1.1 强制ASPM的状态
也可以通过boot的参数，强制enable/disable ASPM：
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
Management.
off Disable ASPM.
force Enable ASPM even on devices that claim not to support it.
WARNING: Forcing ASPM on may cause system lockups.2.2.2 使用enable_aspm使能ASPM
enable_aspm是一个脚本，可以用于启用ASPM。具体你可以阅读如下链接：
- http://drvbp1.linux-foundation.org/~mcgrof/scripts/enable-aspm
只需要修改如下三个参数：
ROOT_COMPLEX="00:1c.1"
ENDPOINT="03:00.0"
# We'll only enable the last 2 bits by using a mask
# of :3 to setpci, this will ensure we keep the existing
# values on the byte.
#
# Hex Binary Meaning
# -------------------------
# 0 0b00 L0 only
# 1 0b01 L0s only
# 2 0b10 L1 only
# 3 0b11 L1 and L0s
ASPM_SETTING=32.2.3 使用setpci使能ASPM
"PCIE Link Control Register"可以通过"lspci -vvv"进行读取，所以可以通过"setpci"工具修改相关寄存器，来使能PCIe ASPM。
2.2.3.1 如何读取"Link Control Register"？
如下是"Link Control Register"中关于ASPM的状态展示：
0b00 = L0 only
0b01 = L0s only
0b10 = L1 only
0b11 = L1 and L0s2.2.3.2 如何找到"Link Control Register"？
首先查找你想要的设备，如下所示：
user@tux ~ $ lspci | grep -i atheros
03:00.0 Network controller: Atheros Communications Inc. Device 0030 (rev 01)03:00.0是总线地址。现在，使用"lspci -t"检查该设备位于哪个RC上。
-[0000:00]-+-00.0
+-02.0
+-02.1
+-03.0
+-03.2
+-03.3
+-19.0
+-1a.0
+-1a.1
+-1a.7
+-1b.0
+-1c.0-[0000:02]--
+-1c.1-[0000:03]----00.0
+-1c.2-[0000:04]--
+-1c.3-[0000:05-0c]--
+-1c.4-[0000:0d-14]--
+-1d.0
+-1d.1
+-1d.2
+-1d.7
+-1e.0-[0000:15-18]--+-00.0
| \-00.1
+-1f.0
+-1f.1
+-1f.2
\-1f.3在这种情况下，我们看到03:00.0位于00:1c.1上，你可以执行"lspci -s 00:1c.1 -xxx"，以获取该设备的PCI配置空间。PCIe规范有一个有趣的小算法，可以从PCI配置空间中找到链路控制寄存器。逻辑如下：
-
Read 0x34 and read the register that points to
-
If that value is not 0x10 then read the next byte (0x35) and go read that register
-
If that register is not 0x10 then read the next byte and go read that register
-
Repeat this until you find a register that has 0x10
-
Once you find the register with 0x10 then add 0x10 to the final register you were reading
-
The Link Control Register is this final register + 0x10 Lets analyze a real world example of a root complex, specifically the one of the root complex above.
user@tux ~ $ sudo lspci -s 00:1c.1 -xxx
00:1c.1 PCI bridge: Intel Corporation 82801H (ICH8 Family) PCI Express Port 2 (rev 03)
00: 86 80 41 28 07 05 10 00 03 00 04 06 10 00 81 00
10: 00 00 00 00 00 00 00 00 00 03 03 00 30 30 00 00
20: 00 dc 30 df e1 df e1 df 00 00 00 00 00 00 00 00
30: 00 00 00 00 40 00 00 00 00 00 00 00 0b 02 04 00
40: 10 80 41 01 c0 8f 00 00 00 00 10 00 11 2c 11 02
50: 40 00 11 30 e0 a0 18 00 00 00 48 01 00 00 00 00
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
80: 05 90 01 00 0c 30 e0 fe 69 41 00 00 00 00 00 00
90: 0d a0 00 00 aa 17 ad 20 00 00 00 00 00 00 00 00
a0: 01 00 02 c8 00 00 00 00 00 00 00 00 00 00 00 00
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 80 00 11 08 00 00 00 00
e0: 00 0f c7 00 06 07 08 00 33 00 00 00 00 00 00 00
f0: 00 00 00 00 00 00 00 00 86 0f 05 00 00 00 00 00首先读取地址0x34，我们看到它是0x40（在这里不要跳到下一个字节）。我们读取0x40，并看到它是0x10。现在我们加上0x40 + 0x10 = 0x50。我们读取0x50。0x50是链路控制寄存器的值。0x50的值是0x40。这意味着只有L0被启用，因此ASPM完全被禁用。要调整此RC的ASPM，我们需要首先保留原始值，然后与我们的新ASPM设置进行OR运算。
注意：事实证明，0x50也用于ICH6、ICH7、ICH8、ICH9的链路控制寄存器。
# Disables ASPM, enables only L0 (this was the existing setting)
sudo setpci -s 00:1c.1 0x50.B=0x40
# Enable L0s only
sudo setpci -s 00:1c.1 0x50.B=0x41
# Enable L1 only
sudo setpci -s 00:1c.1 0x50.B=0x42
# Enable L1 and L0s
sudo setpci -s 00:1c.1 0x50.B=0x43现在，让我们可以调整你的设备。获取到的设备的PCIe配置空间如下所示：
user@tux ~ $ sudo lspci -s 03:00.0 -xxx
03:00.0 Network controller: Atheros Communications Inc. Device 0030 (rev 01)
00: 8c 16 30 00 03 01 10 40 01 00 80 02 10 00 00 00
10: 04 00 3e df 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 8c 16 16 31
30: 00 00 00 00 40 00 00 00 00 00 00 00 0b 01 00 00
40: 01 50 c3 5b 00 00 00 00 00 00 00 00 00 00 00 00
50: 05 70 84 01 00 00 00 00 00 00 00 00 00 00 00 00
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
70: 10 00 02 00 00 87 04 05 10 20 0b 00 11 5c 03 00
80: 41 00 11 10 00 00 00 00 00 00 00 00 00 00 00 00
90: 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00这个例子稍微复杂一些，所以我们将逐行进行分析：
00: 8c 16 30 00 03 01 10 40 01 00 80 02 10 00 00 00
10: 04 00 3e df 00 00 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 8c 16 16 31
30: 00 00 00 00 40 00 00 00 00 00 00 00 0b 01 00 00
^ ^
| |
0x30 0x34
So 0x34 = 0x40. 0x40 is not 0x10 so we go read 0x40 now
40: 01 50 c3 5b 00 00 00 00 00 00 00 00 00 00 00 00
^
|
0x40 = 0x01, this is not 0x10 so read the next byte
40: 01 50 c3 5b 00 00 00 00 00 00 00 00 00 00 00 00
^
|
0x41 = 0x50, so go read that register next
50: 05 70 84 01 00 00 00 00 00 00 00 00 00 00 00 00
^
|
0x50 = 0x05, this is not 0x10, so go read the next byte.
The next byte 0x51 = 0x70 so we go read that register next.
70: 10 00 02 00 00 87 04 05 10 20 0b 00 11 5c 03 00
^
|
At last, 0x70 = 0x10. So now we do 0x70 + 0x10 = 0x80 and go read 0x80.
80: 41 00 11 10 00 00 00 00 00 00 00 00 00 00 00 00
^
|
0x80 = 0x41
0x41 = 0b1000001 so this has ASPM L0s on only.所以，使用如下指令修改PCIe ASPM的状态：
# Disables ASPM, enables only L0
sudo setpci -s 03:00.0 0x80.B=0x40
# Enable L0s only (this was the existing setting)
sudo setpci -s 03:00.0 0x80.B=0x41
# Enable L1 only
sudo setpci -s 03:00.0 0x80.B=0x42
# Enable L1 and L0s
sudo setpci -s 03:00.0 0x80.B=0x43
