PCI: brcmstb: Disable L0s component of ASPM if requested

Some informal internal experiments has shown that the BrcmSTB ASPM L0s
savings may introduce an undesirable noise signal on some customers'
boards.  In addition, L0s was found lacking in realized power savings,
especially relative to the L1 ASPM component.  This is BrcmSTB's
experience and may not hold for others.  At any rate, if the
'aspm-no-l0s' property is present L0s will be disabled.

Link: https://lore.kernel.org/r/20200507201544.43432-5-james.quinlan@broadcom.comSigned-off-by: Jim Quinlan <jquinlan@broadcom.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

drivers/pci/controller/pcie-brcmstb.c

@@ -41,6 +41,9 @@
 #define PCIE_RC_CFG_PRIV1_ID_VAL3			0x043c
 #define  PCIE_RC_CFG_PRIV1_ID_VAL3_CLASS_CODE_MASK	0xffffff
 
+#define PCIE_RC_CFG_PRIV1_LINK_CAPABILITY			0x04dc
+#define  PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_ASPM_SUPPORT_MASK	0xc00
+
 #define PCIE_RC_DL_MDIO_ADDR				0x1100
 #define PCIE_RC_DL_MDIO_WR_DATA				0x1104
 #define PCIE_RC_DL_MDIO_RD_DATA				0x1108
@@ -693,7 +696,7 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
 	int num_out_wins = 0;
 	u16 nlw, cls, lnksta;
 	int i, ret;
-	u32 tmp;
+	u32 tmp, aspm_support;
 
 	/* Reset the bridge */
 	brcm_pcie_bridge_sw_init_set(pcie, 1);
@@ -804,6 +807,15 @@ static int brcm_pcie_setup(struct brcm_pcie *pcie)
 		num_out_wins++;
 	}
 
+	/* Don't advertise L0s capability if 'aspm-no-l0s' */
+	aspm_support = PCIE_LINK_STATE_L1;
+	if (!of_property_read_bool(pcie->np, "aspm-no-l0s"))
+		aspm_support |= PCIE_LINK_STATE_L0S;
+	tmp = readl(base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
+	u32p_replace_bits(&tmp, aspm_support,
+		PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_ASPM_SUPPORT_MASK);
+	writel(tmp, base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
+
 	/*
 	 * For config space accesses on the RC, show the right class for
 	 * a PCIe-PCIe bridge (the default setting is to be EP mode).