[RFC PATCH 2/3] PCI: aardvark: Add support for sending Set_Slot_Power_Limit message

["Pali Rohár" <pali@kernel.org>]

According to PCIe Base specification 3.0, when transitioning from a
non-DL_Up Status to a DL_Up Status, the Port must initiate the
transmission of a Set_Slot_Power_Limit Message to the other component
on the Link to convey the value programmed in the Slot Power Limit
Scale and Value fields of the Slot Capabilities register. This
Transmission is optional if the Slot Capabilities register has not
yet been initialized.

As PCIe Root Bridge is emulated by kernel emulate readback of Slot Power
Limit Scale and Value bits in Slot Capabilities register.

Also send that Set_Slot_Power_Limit message via Message Generation Control
Register in Link Up handler when link changes from down to up state and
slot power limit value was defined.

Slot power limit value is read from DT property 'slot-power-limit' which
value is in mW unit. When this DT property is not specified then it is
treated as "Slot Capabilities register has not yet been initialized".

Signed-off-by: Pali Rohár <pali@kernel.org>
---
 .../devicetree/bindings/pci/aardvark-pci.txt  |  2 +
 drivers/pci/controller/pci-aardvark.c         | 66 ++++++++++++++++++-
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/pci/aardvark-pci.txt b/Documentation/devicetree/bindings/pci/aardvark-pci.txt
index 2b8ca920a7fa..bb658f261db0 100644
--- a/Documentation/devicetree/bindings/pci/aardvark-pci.txt
+++ b/Documentation/devicetree/bindings/pci/aardvark-pci.txt
@@ -20,6 +20,7 @@ contain the following properties:
    define the mapping of the PCIe interface to interrupt numbers.
  - bus-range: PCI bus numbers covered
  - phys: the PCIe PHY handle
+ - slot-power-limit: see pci.txt
  - max-link-speed: see pci.txt
  - reset-gpios: see pci.txt
 
@@ -52,6 +53,7 @@ Example:
 				<0 0 0 3 &pcie_intc 2>,
 				<0 0 0 4 &pcie_intc 3>;
 		phys = <&comphy1 0>;
+		slot-power-limit: <10000>;
 		pcie_intc: interrupt-controller {
 			interrupt-controller;
 			#interrupt-cells = <1>;
diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
index f94898f6072f..cf704c199c15 100644
--- a/drivers/pci/controller/pci-aardvark.c
+++ b/drivers/pci/controller/pci-aardvark.c
@@ -166,6 +166,11 @@
 #define VENDOR_ID_REG				(LMI_BASE_ADDR + 0x44)
 #define DEBUG_MUX_CTRL_REG			(LMI_BASE_ADDR + 0x208)
 #define     DIS_ORD_CHK				BIT(30)
+#define PME_MSG_GEN_CTRL			(LMI_BASE_ADDR + 0x220)
+#define     SEND_SET_SLOT_POWER_LIMIT		BIT(13)
+#define     SEND_PME_TURN_OFF			BIT(14)
+#define     SLOT_POWER_LIMIT_DATA_SHIFT		16
+#define     SLOT_POWER_LIMIT_DATA_MASK		GENMASK(25, 16)
 
 /* PCIe core controller registers */
 #define CTRL_CORE_BASE_ADDR			0x18000
@@ -267,6 +272,7 @@ static bool advk_pcie_link_up(struct advk_pcie *pcie)
 {
 	u32 val, ltssm_state;
 	u16 slotsta, slotctl;
+	u32 slotpwr;
 	bool link_up;
 
 	val = advk_readl(pcie, CFG_REG);
@@ -277,7 +283,25 @@ static bool advk_pcie_link_up(struct advk_pcie *pcie)
 		pcie->link_up = true;
 		slotsta = le16_to_cpu(pcie->bridge.pcie_conf.slotsta);
 		slotctl = le16_to_cpu(pcie->bridge.pcie_conf.slotctl);
+		slotpwr = (le32_to_cpu(pcie->bridge.pcie_conf.slotcap) &
+			   (PCI_EXP_SLTCAP_SPLV | PCI_EXP_SLTCAP_SPLS)) >> 7;
 		pcie->bridge.pcie_conf.slotsta = cpu_to_le16(slotsta | PCI_EXP_SLTSTA_DLLSC);
+		if (!(slotctl & PCI_EXP_SLTCTL_ASPL_DISABLE) && slotpwr) {
+			/*
+			 * According to PCIe Base specification 3.0, when transitioning from a
+			 * non-DL_Up Status to a DL_Up Status, the Port must initiate the
+			 * transmission of a Set_Slot_Power_Limit Message to the other component
+			 * on the Link to convey the value programmed in the Slot Power Limit
+			 * Scale and Value fields of the Slot Capabilities register. This
+			 * Transmission is optional if the Slot Capabilities register has not
+			 * yet been initialized.
+			 */
+			val = advk_readl(pcie, PME_MSG_GEN_CTRL);
+			val &= ~SLOT_POWER_LIMIT_DATA_MASK;
+			val |= slotpwr << SLOT_POWER_LIMIT_DATA_SHIFT;
+			val |= SEND_SET_SLOT_POWER_LIMIT;
+			advk_writel(pcie, val, PME_MSG_GEN_CTRL);
+		}
 		if ((slotctl & PCI_EXP_SLTCTL_DLLSCE) && (slotctl & PCI_EXP_SLTCTL_HPIE))
 			mod_timer(&pcie->link_up_irq_timer, jiffies + 1);
 	}
@@ -956,6 +980,9 @@ static struct pci_bridge_emul_ops advk_pci_bridge_emul_ops = {
 static int advk_sw_pci_bridge_init(struct advk_pcie *pcie)
 {
 	struct pci_bridge_emul *bridge = &pcie->bridge;
+	struct device *dev = &pcie->pdev->dev;
+	u8 slot_power_limit_scale, slot_power_limit_value;
+	u32 slot_power_limit;
 	int ret;
 
 	bridge->conf.vendor =
@@ -988,6 +1015,40 @@ static int advk_sw_pci_bridge_init(struct advk_pcie *pcie)
 	/* Indicates supports for Completion Retry Status */
 	bridge->pcie_conf.rootcap = cpu_to_le16(PCI_EXP_RTCAP_CRSVIS);
 
+	if (of_property_read_u32(dev->of_node, "slot-power-limit", &slot_power_limit))
+		slot_power_limit = 0;
+
+	if (slot_power_limit)
+		dev_info(dev, "Slot power limit %u.%uW\n", slot_power_limit / 1000,
+			 (slot_power_limit / 100) % 10);
+
+	/* Calculate Slot Power Limit Value and Slot Power Limit Scale */
+	if (slot_power_limit == 0) {
+		slot_power_limit_scale = 0;
+		slot_power_limit_value = 0x00;
+	} else if (slot_power_limit <= 255) {
+		slot_power_limit_scale = 3;
+		slot_power_limit_value = slot_power_limit;
+	} else if (slot_power_limit <= 255*10) {
+		slot_power_limit_scale = 2;
+		slot_power_limit_value = slot_power_limit / 10;
+	} else if (slot_power_limit <= 255*100) {
+		slot_power_limit_scale = 1;
+		slot_power_limit_value = slot_power_limit / 100;
+	} else if (slot_power_limit <= 239*1000) {
+		slot_power_limit_scale = 0;
+		slot_power_limit_value = slot_power_limit / 1000;
+	} else if (slot_power_limit <= 250*1000) {
+		slot_power_limit_scale = 0;
+		slot_power_limit_value = 0xF0;
+	} else if (slot_power_limit <= 275*1000) {
+		slot_power_limit_scale = 0;
+		slot_power_limit_value = 0xF1;
+	} else {
+		slot_power_limit_scale = 0;
+		slot_power_limit_value = 0xF2;
+	}
+
 	/*
 	 * Mark bridge as Hot-Plug Capable to allow delivering Data Link Layer
 	 * State Changed interrupt. No Command Completed Support is set because
@@ -996,7 +1057,10 @@ static int advk_sw_pci_bridge_init(struct advk_pcie *pcie)
 	 * bit permanently as there is no support for unplugging PCIe card from
 	 * the slot. Assume that PCIe card is always connected in slot.
 	 */
-	bridge->pcie_conf.slotcap = cpu_to_le32(PCI_EXP_SLTCAP_NCCS | PCI_EXP_SLTCAP_HPC);
+	bridge->pcie_conf.slotcap = cpu_to_le32(PCI_EXP_SLTCAP_NCCS |
+						PCI_EXP_SLTCAP_HPC |
+						slot_power_limit_value << 7 |
+						slot_power_limit_scale << 15);
 	bridge->pcie_conf.slotsta = cpu_to_le16(PCI_EXP_SLTSTA_PDS);
 
 	return 0;
-- 
2.20.1