PCI: brcmstb: Configure HW CLKREQ# mode appropriate for downstream device

The Broadcom STB/CM PCIe HW core, which is also used in RPi SOCs, must be
deliberately set by the PCIe RC HW into one of three mutually exclusive
modes:

"safe" -- No CLKREQ# expected or required, refclk is always provided.  This
    mode should work for all devices but is not be capable of any refclk
    power savings.

"no-l1ss" -- CLKREQ# is expected to be driven by the downstream device for
    CPM and ASPM L0s and L1.  Provides Clock Power Management, L0s, and L1,
    but cannot provide L1 substate (L1SS) power savings. If the downstream
    device connected to the RC is L1SS capable AND the OS enables L1SS, all
    PCIe traffic may abruptly halt, potentially hanging the system.

"default" -- Bidirectional CLKREQ# between the RC and downstream device.
    Provides ASPM L0s, L1, and L1SS, but not compliant to provide Clock
    Power Management; specifically, may not be able to meet the T_CLRon max
    timing of 400ns as specified in "Dynamic Clock Control", section
    3.2.5.2.2 of the PCIe Express Mini CEM 2.1 specification.  This
    situation is atypical and should happen only with older devices.

Previously, this driver always set the mode to "no-l1ss", as almost all
STB/CM boards operate in this mode.  But now there is interest in
activating L1SS power savings from STB/CM customers, which requires "aspm"
mode.  In addition, a bug was filed for RPi4 CM platform because most
devices did not work in "no-l1ss" mode.

Note that the mode is specified by the DT property "brcm,clkreq-mode".  If
this property is omitted, then "default" mode is chosen.

Note: Since L1 substates are now possible, a modification was made
regarding an internal bus timeout: During long periods of the PCIe RC HW
being in an L1SS sleep state, there may be a timeout on an internal bus
access, even though there may not be any PCIe access involved.  Such a
timeout will cause a subsequent CPU abort.

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217276
Link: https://lore.kernel.org/linux-pci/20231113185607.1756-3-james.quinlan@broadcom.com
Tested-by: Cyril Brulebois <cyril@debamax.com>
Tested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>

1 files changed, 86 insertions, 10 deletions

diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
index f9dd6622fe10..5b0730c3891b 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c
@@ -48,6 +48,9 @@
 #define PCIE_RC_CFG_PRIV1_LINK_CAPABILITY			0x04dc
 #define  PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_ASPM_SUPPORT_MASK	0xc00
 
+#define PCIE_RC_CFG_PRIV1_ROOT_CAP			0x4f8
+#define  PCIE_RC_CFG_PRIV1_ROOT_CAP_L1SS_MODE_MASK	0xf8
+
 #define PCIE_RC_DL_MDIO_ADDR				0x1100
 #define PCIE_RC_DL_MDIO_WR_DATA				0x1104
 #define PCIE_RC_DL_MDIO_RD_DATA				0x1108
@@ -121,9 +124,12 @@
 
 #define PCIE_MISC_HARD_PCIE_HARD_DEBUG					0x4204
 #define  PCIE_MISC_HARD_PCIE_HARD_DEBUG_CLKREQ_DEBUG_ENABLE_MASK	0x2
+#define  PCIE_MISC_HARD_PCIE_HARD_DEBUG_L1SS_ENABLE_MASK		0x200000
 #define  PCIE_MISC_HARD_PCIE_HARD_DEBUG_SERDES_IDDQ_MASK		0x08000000
 #define  PCIE_BMIPS_MISC_HARD_PCIE_HARD_DEBUG_SERDES_IDDQ_MASK		0x00800000
-
+#define  PCIE_CLKREQ_MASK \
+	  (PCIE_MISC_HARD_PCIE_HARD_DEBUG_CLKREQ_DEBUG_ENABLE_MASK | \
+	   PCIE_MISC_HARD_PCIE_HARD_DEBUG_L1SS_ENABLE_MASK)
 
 #define PCIE_INTR2_CPU_BASE		0x4300
 #define PCIE_MSI_INTR2_BASE		0x4500
@@ -1028,13 +1034,89 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
 	return 0;
 }
 
+/*
+ * This extends the timeout period for an access to an internal bus.  This
+ * access timeout may occur during L1SS sleep periods, even without the
+ * presence of a PCIe access.
+ */
+static void brcm_extend_rbus_timeout(struct brcm_pcie *pcie)
+{
+	/* TIMEOUT register is two registers before RGR1_SW_INIT_1 */
+	const unsigned int REG_OFFSET = PCIE_RGR1_SW_INIT_1(pcie) - 8;
+	u32 timeout_us = 4000000; /* 4 seconds, our setting for L1SS */
+
+	/* Each unit in timeout register is 1/216,000,000 seconds */
+	writel(216 * timeout_us, pcie->base + REG_OFFSET);
+}
+
+static void brcm_config_clkreq(struct brcm_pcie *pcie)
+{
+	static const char err_msg[] = "invalid 'brcm,clkreq-mode' DT string\n";
+	const char *mode = "default";
+	u32 clkreq_cntl;
+	int ret, tmp;
+
+	ret = of_property_read_string(pcie->np, "brcm,clkreq-mode", &mode);
+	if (ret && ret != -EINVAL) {
+		dev_err(pcie->dev, err_msg);
+		mode = "safe";
+	}
+
+	/* Start out assuming safe mode (both mode bits cleared) */
+	clkreq_cntl = readl(pcie->base + PCIE_MISC_HARD_PCIE_HARD_DEBUG);
+	clkreq_cntl &= ~PCIE_CLKREQ_MASK;
+
+	if (strcmp(mode, "no-l1ss") == 0) {
+		/*
+		 * "no-l1ss" -- Provides Clock Power Management, L0s, and
+		 * L1, but cannot provide L1 substate (L1SS) power
+		 * savings. If the downstream device connected to the RC is
+		 * L1SS capable AND the OS enables L1SS, all PCIe traffic
+		 * may abruptly halt, potentially hanging the system.
+		 */
+		clkreq_cntl |= PCIE_MISC_HARD_PCIE_HARD_DEBUG_CLKREQ_DEBUG_ENABLE_MASK;
+		/*
+		 * We want to un-advertise L1 substates because if the OS
+		 * tries to configure the controller into using L1 substate
+		 * power savings it may fail or hang when the RC HW is in
+		 * "no-l1ss" mode.
+		 */
+		tmp = readl(pcie->base + PCIE_RC_CFG_PRIV1_ROOT_CAP);
+		u32p_replace_bits(&tmp, 2, PCIE_RC_CFG_PRIV1_ROOT_CAP_L1SS_MODE_MASK);
+		writel(tmp, pcie->base + PCIE_RC_CFG_PRIV1_ROOT_CAP);
+
+	} else if (strcmp(mode, "default") == 0) {
+		/*
+		 * "default" -- Provides L0s, L1, and L1SS, but not
+		 * compliant to provide Clock Power Management;
+		 * specifically, may not be able to meet the Tclron max
+		 * timing of 400ns as specified in "Dynamic Clock Control",
+		 * section 3.2.5.2.2 of the PCIe spec.  This situation is
+		 * atypical and should happen only with older devices.
+		 */
+		clkreq_cntl |= PCIE_MISC_HARD_PCIE_HARD_DEBUG_L1SS_ENABLE_MASK;
+		brcm_extend_rbus_timeout(pcie);
+
+	} else {
+		/*
+		 * "safe" -- No power savings; refclk is driven by RC
+		 * unconditionally.
+		 */
+		if (strcmp(mode, "safe") != 0)
+			dev_err(pcie->dev, err_msg);
+		mode = "safe";
+	}
+	writel(clkreq_cntl, pcie->base + PCIE_MISC_HARD_PCIE_HARD_DEBUG);
+
+	dev_info(pcie->dev, "clkreq-mode set to %s\n", mode);
+}
+
 static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 {
 	struct device *dev = pcie->dev;
 	void __iomem *base = pcie->base;
 	u16 nlw, cls, lnksta;
 	bool ssc_good = false;
-	u32 tmp;
 	int ret, i;
 
 	/* Unassert the fundamental reset */
@@ -1059,6 +1141,8 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 		return -ENODEV;
 	}
 
+	brcm_config_clkreq(pcie);
+
 	if (pcie->gen)
 		brcm_pcie_set_gen(pcie, pcie->gen);
 
@@ -1077,14 +1161,6 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 		 pci_speed_string(pcie_link_speed[cls]), nlw,
 		 ssc_good ? "(SSC)" : "(!SSC)");
 
-	/*
-	 * Refclk from RC should be gated with CLKREQ# input when ASPM L0s,L1
-	 * is enabled => setting the CLKREQ_DEBUG_ENABLE field to 1.
-	 */
-	tmp = readl(base + PCIE_MISC_HARD_PCIE_HARD_DEBUG);
-	tmp |= PCIE_MISC_HARD_PCIE_HARD_DEBUG_CLKREQ_DEBUG_ENABLE_MASK;
-	writel(tmp, base + PCIE_MISC_HARD_PCIE_HARD_DEBUG);
-
 	return 0;
 }