PCI: add PCI Express ASPM support

PCI Express ASPM defines a protocol for PCI Express components in the D0
state to reduce Link power by placing their Links into a low power state
and instructing the other end of the Link to do likewise. This
capability allows hardware-autonomous, dynamic Link power reduction
beyond what is achievable by software-only controlled power management.
However, The device should be configured by software appropriately.
Enabling ASPM will save power, but will introduce device latency.

This patch adds ASPM support in Linux. It introduces a global policy for
ASPM, a sysfs file /sys/module/pcie_aspm/parameters/policy can control
it. The interface can be used as a boot option too. Currently we have
below setting:
        -default, BIOS default setting
        -powersave, highest power saving mode, enable all available ASPM
state and clock power management
        -performance, highest performance, disable ASPM and clock power
management
By default, the 'default' policy is used currently.

In my test, power difference between powersave mode and performance mode
is about 1.3w in a system with 3 PCIE links.

Note: some devices might not work well with aspm, either because chipset
issue or device issue. The patch provide API (pci_disable_link_state),
driver can disable ASPM for specific device.

Signed-off-by: Shaohua Li <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

drivers/pci/pci-sysfs.c

@@ -21,6 +21,7 @@
 #include <linux/topology.h>
 #include <linux/mm.h>
 #include <linux/capability.h>
+#include <linux/pci-aspm.h>
 #include "pci.h"
 
 static int sysfs_initialized;	/* = 0 */
@@ -650,6 +651,8 @@ int __must_check pci_create_sysfs_dev_files (struct pci_dev *pdev)
 	if (pcibios_add_platform_entries(pdev))
 		goto err_rom_file;
 
+	pcie_aspm_create_sysfs_dev_files(pdev);
+
 	return 0;
 
 err_rom_file:
@@ -679,6 +682,8 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
 	if (!sysfs_initialized)
 		return;
 
+	pcie_aspm_remove_sysfs_dev_files(pdev);
+
 	if (pdev->cfg_size < 4096)
 		sysfs_remove_bin_file(&pdev->dev.kobj, &pci_config_attr);
 	else

drivers/pci/pci.c

@@ -18,6 +18,7 @@
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/log2.h>
+#include <linux/pci-aspm.h>
 #include <asm/dma.h>	/* isa_dma_bridge_buggy */
 #include "pci.h"
 
@@ -501,6 +502,9 @@ pci_set_power_state(struct pci_dev *dev, pci_power_t state)
 	if (need_restore)
 		pci_restore_bars(dev);
 
+	if (dev->bus->self)
+		pcie_aspm_pm_state_change(dev->bus->self);
+
 	return 0;
 }
 

drivers/pci/pcie/Kconfig

@@ -26,3 +26,23 @@ config HOTPLUG_PCI_PCIE
 	  When in doubt, say N.
 
 source "drivers/pci/pcie/aer/Kconfig"
+
+#
+# PCI Express ASPM
+#
+config PCIEASPM
+	bool "PCI Express ASPM support(Experimental)"
+	depends on PCI && EXPERIMENTAL && PCIEPORTBUS
+	default y
+	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.
+config PCIEASPM_DEBUG
+	bool "Debug PCI Express ASPM"
+	depends on PCIEASPM
+	default n
+	help
+	  This enables PCI Express ASPM debug support. It will add per-device
+	  interface to control ASPM.

drivers/pci/pcie/Makefile

@@ -2,6 +2,9 @@
 # Makefile for PCI-Express PORT Driver
 #
 
+# Build PCI Express ASPM if needed
+obj-$(CONFIG_PCIEASPM)		+= aspm.o
+
 pcieportdrv-y			:= portdrv_core.o portdrv_pci.o portdrv_bus.o
 
 obj-$(CONFIG_PCIEPORTBUS)	+= pcieportdrv.o