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Message-ID: <20251028134601.3688030-1-s-vadapalli@ti.com>
Date: Tue, 28 Oct 2025 19:15:58 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: <lpieralisi@...nel.org>, <kwilczynski@...nel.org>, <mani@...nel.org>,
<robh@...nel.org>, <bhelgaas@...gle.com>, <kishon@...nel.org>,
<18255117159@....com>, <unicorn_wang@...look.com>
CC: <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>, <srk@...com>, <s-vadapalli@...com>
Subject: [PATCH v2] PCI: cadence: Enable support for applying lane equalization presets
The PCIe Link Equalization procedure allows peers on a PCIe Link to
improve the signal quality by exchanging transmitter presets and
receiver preset hints in the form of Ordered Sets.
For link speeds of 8.0 GT/s and above, the transmitter presets and the
receiver preset hints are configurable parameters which can be tuned to
establish a stable link. This allows setting up a stable link that is
specific to the peers across a Link.
The device-tree property 'eq-presets-Ngts' (eq-presets-8gts,
eq-presets-16gts, ...) specifies the transmitter presets and receiver
preset hints to be applied to every lane of the link for every supported
link speed that is greater than or equal to 8.0 GT/s.
Hence, enable support for applying the 'optional' lane equalization
presets when operating in the Root-Port (Root-Complex / Host) mode.
Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
---
Hello,
This patch is based on linux-next tagged next-20251028.
It also applies cleanly on v6.18-rc1.
Link to v1 patch:
https://lore.kernel.org/r/20251027133013.2589119-1-s-vadapalli@ti.com/
Changes since v1:
- Implemented Bjorn's suggestion of adding 'fallthrough' keyword in
switch-case to avoid compilation warnings, since 'fallthrough' is
intentional.
Regards,
Siddharth.
.../controller/cadence/pcie-cadence-host.c | 85 +++++++++++++++++++
drivers/pci/controller/cadence/pcie-cadence.h | 5 ++
2 files changed, 90 insertions(+)
diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
index fffd63d6665e..ae85ad8cce82 100644
--- a/drivers/pci/controller/cadence/pcie-cadence-host.c
+++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
@@ -168,6 +168,90 @@ static void cdns_pcie_host_enable_ptm_response(struct cdns_pcie *pcie)
cdns_pcie_writel(pcie, CDNS_PCIE_LM_PTM_CTRL, val | CDNS_PCIE_LM_TPM_CTRL_PTMRSEN);
}
+static void cdns_pcie_setup_lane_equalization_presets(struct cdns_pcie_rc *rc)
+{
+ struct cdns_pcie *pcie = &rc->pcie;
+ struct device *dev = pcie->dev;
+ struct device_node *np = dev->of_node;
+ int max_link_speed, max_lanes, ret;
+ u32 lane_eq_ctrl_reg;
+ u16 cap;
+ u16 *presets_8gts;
+ u8 *presets_ngts;
+ u8 i, j;
+
+ ret = of_property_read_u32(np, "num-lanes", &max_lanes);
+ if (ret)
+ return;
+
+ /* Lane Equalization presets are optional, so error message is not necessary */
+ ret = of_pci_get_equalization_presets(dev, &rc->eq_presets, max_lanes);
+ if (ret)
+ return;
+
+ max_link_speed = of_pci_get_max_link_speed(np);
+ if (max_link_speed < 0) {
+ dev_err(dev, "%s: link-speed unknown, skipping preset setup\n", __func__);
+ return;
+ }
+
+ /*
+ * Setup presets for data rates including and upward of 8.0 GT/s until the
+ * maximum supported data rate.
+ */
+ switch (pcie_link_speed[max_link_speed]) {
+ case PCIE_SPEED_16_0GT:
+ presets_ngts = (u8 *)rc->eq_presets.eq_presets_Ngts[EQ_PRESET_TYPE_16GTS - 1];
+ if (presets_ngts[0] != PCI_EQ_RESV) {
+ cap = cdns_pcie_find_ext_capability(pcie, PCI_EXT_CAP_ID_PL_16GT);
+ if (!cap)
+ break;
+ lane_eq_ctrl_reg = cap + PCI_PL_16GT_LE_CTRL;
+ /*
+ * For Link Speeds including and upward of 16.0 GT/s, the Lane Equalization
+ * Control register has the following layout per Lane:
+ * Bits 0-3: Downstream Port Transmitter Preset
+ * Bits 4-7: Upstream Port Transmitter Preset
+ *
+ * 'eq_presets_Ngts' is an array of u8 (byte).
+ * Therefore, we need to write to the Lane Equalization Control
+ * register in units of bytes per-Lane.
+ */
+ for (i = 0; i < max_lanes; i++)
+ cdns_pcie_rp_writeb(pcie, lane_eq_ctrl_reg + i, presets_ngts[i]);
+
+ dev_info(dev, "Link Equalization presets applied for 16.0 GT/s\n");
+ }
+ fallthrough;
+ case PCIE_SPEED_8_0GT:
+ presets_8gts = (u16 *)rc->eq_presets.eq_presets_8gts;
+ if ((presets_8gts[0] & PCI_EQ_RESV) != PCI_EQ_RESV) {
+ cap = cdns_pcie_find_ext_capability(pcie, PCI_EXT_CAP_ID_SECPCI);
+ if (!cap)
+ break;
+ lane_eq_ctrl_reg = cap + PCI_SECPCI_LE_CTRL;
+ /*
+ * For a Link Speed of 8.0 GT/s, the Lane Equalization Control register has
+ * the following layout per Lane:
+ * Bits 0-3: Downstream Port Transmitter Preset
+ * Bits 4-6: Downstream Port Receiver Preset Hint
+ * Bit 7: Reserved
+ * Bits 8-11: Upstream Port Transmitter Preset
+ * Bits 12-14: Upstream Port Receiver Preset Hint
+ * Bit 15: Reserved
+ *
+ * 'eq_presets_8gts' is an array of u16 (word).
+ * Therefore, we need to write to the Lane Equalization Control
+ * register in units of words per-Lane.
+ */
+ for (i = 0, j = 0; i < max_lanes; i++, j += 2)
+ cdns_pcie_rp_writew(pcie, lane_eq_ctrl_reg + j, presets_8gts[i]);
+
+ dev_info(dev, "Link Equalization presets applied for 8.0 GT/s\n");
+ }
+ }
+}
+
static int cdns_pcie_host_start_link(struct cdns_pcie_rc *rc)
{
struct cdns_pcie *pcie = &rc->pcie;
@@ -600,6 +684,7 @@ int cdns_pcie_host_link_setup(struct cdns_pcie_rc *rc)
cdns_pcie_detect_quiet_min_delay_set(&rc->pcie);
cdns_pcie_host_enable_ptm_response(pcie);
+ cdns_pcie_setup_lane_equalization_presets(rc);
ret = cdns_pcie_start_link(pcie);
if (ret) {
diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
index e2a853d2c0ab..39d03b309978 100644
--- a/drivers/pci/controller/cadence/pcie-cadence.h
+++ b/drivers/pci/controller/cadence/pcie-cadence.h
@@ -11,6 +11,8 @@
#include <linux/pci-epf.h>
#include <linux/phy/phy.h>
+#include "../../pci.h"
+
/* Parameters for the waiting for link up routine */
#define LINK_WAIT_MAX_RETRIES 10
#define LINK_WAIT_USLEEP_MIN 90000
@@ -288,6 +290,8 @@ struct cdns_pcie {
* available
* @quirk_retrain_flag: Retrain link as quirk for PCIe Gen2
* @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
+ * @eq_presets: Lane Equalization presets for Link Speed including and upward
+ * of 8.0 GT/s
*/
struct cdns_pcie_rc {
struct cdns_pcie pcie;
@@ -298,6 +302,7 @@ struct cdns_pcie_rc {
bool avail_ib_bar[CDNS_PCIE_RP_MAX_IB];
unsigned int quirk_retrain_flag:1;
unsigned int quirk_detect_quiet_flag:1;
+ struct pci_eq_presets eq_presets;
};
/**
--
2.51.0
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