[PATCH v2] PCI: add support for Immediate Readiness

[Felipe Balbi <felipe.balbi@linux.intel.com>]

PCIe GEN4 defines, on section 7.5.1.1.4, a new bit on Status Register
which tells us that:

"Immediate Readiness – This optional bit, when Set, indicates the
Function is guaranteed to be ready to successfully complete valid
configuration accesses at any time following any reset that the host
is capable of issuing Configuration Requests to this Function.

When this bit is Set, for accesses to this Function, software is
exempt from all requirements to delay configuration accesses following
any type of reset, including but not limited to the timing
requirements defined in Section 6.6.  How this guarantee is
established is beyond the scope of this document.

It is permitted that system software/firmware provide mechanisms that
supersede the indication provided by this bit, however such
software/firmware mechanisms are outside the scope of this
specification."

This means that all delays after a Conventional or Function Reset can
be skipped.

This patch reads such bit and caches its value in a flag inside struct
pci_dev to be checked later if we should delay or can skip delays
after a reset. While at that, also move the explicit msleep(100) call
from pcie_flr() and pci_af_flr() to pci_dev_wait().

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
---

changes since v1:
	- rename immediate flag to imm_ready
	- move imm_ready check to pci_flr() and pci_af_flr()


 drivers/pci/pci.c             | 14 +++++++++++++-
 include/linux/pci.h           |  1 +
 include/uapi/linux/pci_regs.h |  1 +
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 29ff9619b5fa..f94e07262ffa 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -999,7 +999,7 @@ static void __pci_start_power_transition(struct pci_dev *dev, pci_power_t state)
 		 * because have already delayed for the bridge.
 		 */
 		if (dev->runtime_d3cold) {
-			if (dev->d3cold_delay)
+			if (dev->d3cold_delay && !dev->imm_ready)
 				msleep(dev->d3cold_delay);
 			/*
 			 * When powering on a bridge from D3cold, the
@@ -2644,6 +2644,7 @@ EXPORT_SYMBOL_GPL(pci_d3cold_disable);
 void pci_pm_init(struct pci_dev *dev)
 {
 	int pm;
+	u16 status;
 	u16 pmc;
 
 	pm_runtime_forbid(&dev->dev);
@@ -2706,6 +2707,11 @@ void pci_pm_init(struct pci_dev *dev)
 		/* Disable the PME# generation functionality */
 		pci_pme_active(dev, false);
 	}
+
+	pci_read_config_word(dev, PCI_STATUS, &status);
+
+	if (status & PCI_STATUS_IMMEDIATE)
+		dev->imm_ready = 1;
 }
 
 static unsigned long pci_ea_flags(struct pci_dev *dev, u8 prop)
@@ -4376,6 +4382,9 @@ int pcie_flr(struct pci_dev *dev)
 
 	pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_BCR_FLR);
 
+	if (dev->imm_ready)
+		return 0;
+
 	/*
 	 * Per PCIe r4.0, sec 6.6.2, a device must complete an FLR within
 	 * 100ms, but may silently discard requests while the FLR is in
@@ -4417,6 +4426,9 @@ static int pci_af_flr(struct pci_dev *dev, int probe)
 
 	pci_write_config_byte(dev, pos + PCI_AF_CTRL, PCI_AF_CTRL_FLR);
 
+	if (dev->imm_ready)
+		return 0;
+
 	/*
 	 * Per Advanced Capabilities for Conventional PCI ECN, 13 April 2006,
 	 * updated 27 July 2006; a device must complete an FLR within
diff --git a/include/linux/pci.h b/include/linux/pci.h
index e72ca8dd6241..7eed464e844a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -325,6 +325,7 @@ struct pci_dev {
 	pci_power_t	current_state;	/* Current operating state. In ACPI,
 					   this is D0-D3, D0 being fully
 					   functional, and D3 being off. */
+	unsigned int	imm_ready:1;	/* Supports Immediate Readiness */
 	u8		pm_cap;		/* PM capability offset */
 	unsigned int	pme_support:5;	/* Bitmask of states from which PME#
 					   can be generated */
diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
index ee556ccc93f4..b5cf51a06cae 100644
--- a/include/uapi/linux/pci_regs.h
+++ b/include/uapi/linux/pci_regs.h
@@ -52,6 +52,7 @@
 #define  PCI_COMMAND_INTX_DISABLE 0x400 /* INTx Emulation Disable */
 
 #define PCI_STATUS		0x06	/* 16 bits */
+#define  PCI_STATUS_IMMEDIATE	0x01	/* Immediate Readiness */
 #define  PCI_STATUS_INTERRUPT	0x08	/* Interrupt status */
 #define  PCI_STATUS_CAP_LIST	0x10	/* Support Capability List */
 #define  PCI_STATUS_66MHZ	0x20	/* Support 66 MHz PCI 2.1 bus */
-- 
2.18.0