linux-kernel - [PATCH 2/8] PCI/bwctrl: Add support to scale bandwidth before & after link re-training

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Message-Id: <20250217-mhi_bw_up-v1-2-9bad1e42bdb1@oss.qualcomm.com>
Date: Mon, 17 Feb 2025 12:04:09 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        Jeff Johnson <jjohnson@...nel.org>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, mhi@...ts.linux.dev,
        linux-wireless@...r.kernel.org, ath11k@...ts.infradead.org,
        quic_jjohnson@...cinc.com, quic_pyarlaga@...cinc.com,
        quic_vbadigan@...cinc.com, quic_vpernami@...cinc.com,
        quic_mrana@...cinc.com,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: [PATCH 2/8] PCI/bwctrl: Add support to scale bandwidth before &
 after link re-training

If the driver wants to move to higher data rate/speed than the current data
rate then the controller driver may need to change certain votes so that
link may come up at requested data rate/speed like QCOM PCIe controllers
need to change their RPMh (Resource Power Manager-hardened) state. Once
link retraining is done controller drivers needs to adjust their votes
based on the final data rate.

Some controllers also may need to update their bandwidth voting like
ICC bw votings etc.

So, add pre_scale_bus_bw() & post_scale_bus_bw() op to call before & after
the link re-train.

In case of PCIe switch, if there is a request to change target speed for a
downstream port then no need to call these function ops as these are
outside the scope of the controller drivers.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
---
 drivers/pci/pcie/bwctrl.c | 15 +++++++++++++++
 include/linux/pci.h       |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 0a5e7efbce2c..e3faa4d1f935 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -161,6 +161,8 @@ static int pcie_bwctrl_change_speed(struct pci_dev *port, u16 target_speed, bool
 int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
 			  bool use_lt)
 {
+	struct pci_host_bridge *host = pci_find_host_bridge(port->bus);
+	bool is_root = pci_is_root_bus(port->bus);
 	struct pci_bus *bus = port->subordinate;
 	u16 target_speed;
 	int ret;
@@ -173,6 +175,16 @@ int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
 
 	target_speed = pcie_bwctrl_select_speed(port, speed_req);
 
+	/*
+	 * The controller driver may need to be scaled for targeted speed
+	 * otherwise link might not come up at requested speed.
+	 */
+	if (is_root && host->ops->pre_scale_bus_bw) {
+		ret = host->ops->pre_scale_bus_bw(host->bus, target_speed);
+		if (ret)
+			return ret;
+	}
+
 	scoped_guard(rwsem_read, &pcie_bwctrl_setspeed_rwsem) {
 		struct pcie_bwctrl_data *data = port->link_bwctrl;
 
@@ -197,6 +209,9 @@ int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
 	    !list_empty(&bus->devices))
 		ret = -EAGAIN;
 
+	if (is_root && host->ops->post_scale_bus_bw)
+		host->ops->post_scale_bus_bw(host->bus, pci_bus_speed2lnkctl2(bus->cur_bus_speed));
+
 	return ret;
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 47b31ad724fa..58f1de626c37 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -804,6 +804,8 @@ struct pci_ops {
 	void __iomem *(*map_bus)(struct pci_bus *bus, unsigned int devfn, int where);
 	int (*read)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 *val);
 	int (*write)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 val);
+	int (*pre_scale_bus_bw)(struct pci_bus *bus, int target_speed);
+	void (*post_scale_bus_bw)(struct pci_bus *bus, int current_speed);
 };
 
 /*

-- 
2.34.1