linux-kernel - [PATCH v1 1/6] PCI: brcmstb: Refactor max speed limit functionality

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Message-ID: <20250205191213.29202-2-james.quinlan@broadcom.com>
Date: Wed,  5 Feb 2025 14:12:01 -0500
From: Jim Quinlan <james.quinlan@...adcom.com>
To: linux-pci@...r.kernel.org,
	Nicolas Saenz Julienne <nsaenz@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Cyril Brulebois <kibi@...ian.org>,
	Stanimir Varbanov <svarbanov@...e.de>,
	bcm-kernel-feedback-list@...adcom.com,
	jim2101024@...il.com,
	james.quinlan@...adcom.com
Cc: Florian Fainelli <florian.fainelli@...adcom.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Rob Herring <robh@...nel.org>,
	linux-rpi-kernel@...ts.infradead.org (moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE),
	linux-arm-kernel@...ts.infradead.org (moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v1 1/6] PCI: brcmstb: Refactor max speed limit functionality

Make changes to the code that limits the PCIe max speed.

(1) Do the changes before link-up, not after.  We do not want
    to temporarily rise to a higher speed than desired.
(2) Use constants from pci_reg.h when possible
(3) Use uXX_replace_bits(...) for setting a register field.
(4) Use the internal link capabilities register for writing
    the max speed, not the official config space register
    where the speed field is RO.  Updating this field is
    not necessary to limit the speed so this mistake was
    harmless.

Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
---
 drivers/pci/controller/pcie-brcmstb.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
index 546056f7f0d3..f8fc3d620ee2 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c
@@ -47,6 +47,7 @@
 
 #define PCIE_RC_CFG_PRIV1_LINK_CAPABILITY			0x04dc
 #define  PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_ASPM_SUPPORT_MASK	0xc00
+#define  PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_MAX_LINK_SPEED_MASK	0xf
 
 #define PCIE_RC_CFG_PRIV1_ROOT_CAP			0x4f8
 #define  PCIE_RC_CFG_PRIV1_ROOT_CAP_L1SS_MODE_MASK	0xf8
@@ -413,12 +414,12 @@ static int brcm_pcie_set_ssc(struct brcm_pcie *pcie)
 static void brcm_pcie_set_gen(struct brcm_pcie *pcie, int gen)
 {
 	u16 lnkctl2 = readw(pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCTL2);
-	u32 lnkcap = readl(pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCAP);
+	u32 lnkcap = readl(pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
 
-	lnkcap = (lnkcap & ~PCI_EXP_LNKCAP_SLS) | gen;
-	writel(lnkcap, pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCAP);
+	u32p_replace_bits(&lnkcap, gen, PCIE_RC_CFG_PRIV1_LINK_CAPABILITY_MAX_LINK_SPEED_MASK);
+	writel(lnkcap, pcie->base + PCIE_RC_CFG_PRIV1_LINK_CAPABILITY);
 
-	lnkctl2 = (lnkctl2 & ~0xf) | gen;
+	u16p_replace_bits(&lnkctl2, gen, PCI_EXP_LNKCTL2_TLS);
 	writew(lnkctl2, pcie->base + BRCM_PCIE_CAP_REGS + PCI_EXP_LNKCTL2);
 }
 
@@ -1324,6 +1325,10 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 	bool ssc_good = false;
 	int ret, i;
 
+	/* Limit the generation if specified */
+	if (pcie->gen)
+		brcm_pcie_set_gen(pcie, pcie->gen);
+
 	/* Unassert the fundamental reset */
 	ret = pcie->cfg->perst_set(pcie, 0);
 	if (ret)
@@ -1350,9 +1355,6 @@ static int brcm_pcie_start_link(struct brcm_pcie *pcie)
 
 	brcm_config_clkreq(pcie);
 
-	if (pcie->gen)
-		brcm_pcie_set_gen(pcie, pcie->gen);
-
 	if (pcie->ssc) {
 		ret = brcm_pcie_set_ssc(pcie);
 		if (ret == 0)
-- 
2.43.0