linux-kernel - [PATCH v4 02/11] PCI/bwctrl: Add support to scale bandwidth before & after link re-training

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Message-Id: <20250609-mhi_bw_up-v4-2-3faa8fe92b05@qti.qualcomm.com>
Date: Mon, 09 Jun 2025 16:21:23 +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>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>, Jeff Johnson <jjohnson@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...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,
        qiang.yu@....qualcomm.com, quic_vbadigan@...cinc.com,
        quic_vpernami@...cinc.com, quic_mrana@...cinc.com,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
        Jeff Johnson <jeff.johnson@....qualcomm.com>
Subject: [PATCH v4 02/11] 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_link_speed_change() & post_link_speed_change() op to call
before & after the link re-train. There is no explicit locking mechanisms
as these are called by a single client Endpoint driver.

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       | 18 ++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 36f939f23d34e8a3b25a2d1b9059e015f298ca94..dafb8d4f1cfba987e1ff08edfc7caba527f0c76b 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -140,6 +140,8 @@ 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_rootbus = pci_is_root_bus(port->bus);
 	struct pci_bus *bus = port->subordinate;
 	u16 target_speed;
 	int ret;
@@ -152,6 +154,16 @@ 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 host bridge driver may need to be scaled for targeted speed
+	 * otherwise link might not come up at requested speed.
+	 */
+	if (is_rootbus && host->pre_link_speed_change) {
+		ret = host->pre_link_speed_change(host, port, target_speed);
+		if (ret)
+			return ret;
+	}
+
 	scoped_guard(rwsem_read, &pcie_bwctrl_setspeed_rwsem) {
 		struct pcie_bwctrl_data *data = port->link_bwctrl;
 
@@ -176,6 +188,9 @@ int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
 	    !list_empty(&bus->devices))
 		ret = -EAGAIN;
 
+	if (bus && is_rootbus && host->post_link_speed_change)
+		host->post_link_speed_change(host, port, pci_bus_speed2lnkctl2(bus->cur_bus_speed));
+
 	return ret;
 }
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 05e68f35f39238f8b9ce08df97b384d1c1e89bbe..1740bab514b0a9a61c027463a1fb154843312a22 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -599,6 +599,24 @@ struct pci_host_bridge {
 	void (*release_fn)(struct pci_host_bridge *);
 	int (*enable_device)(struct pci_host_bridge *bridge, struct pci_dev *dev);
 	void (*disable_device)(struct pci_host_bridge *bridge, struct pci_dev *dev);
+	/*
+	 * Callback to the host bridge drivers to update ICC BW votes, clock
+	 * frequencies etc.. for the link re-train to come up in targeted speed.
+	 * These are intended to be called by devices directly attached to the
+	 * Root Port. These are called by a single client Endpoint driver, so
+	 * there is no need for explicit locking mechanisms.
+	 */
+	int (*pre_link_speed_change)(struct pci_host_bridge *bridge,
+				     struct pci_dev *dev, int speed);
+	/*
+	 * Callback to the host bridge drivers to adjust ICC BW votes, clock
+	 * frequencies etc.. to the updated speed after link re-train. These
+	 * are intended to be called by devices directly attached to the
+	 * Root Port. These are called by a single client Endpoint driver,
+	 * so there is no need for explicit locking mechanisms.
+	 */
+	void (*post_link_speed_change)(struct pci_host_bridge *bridge,
+				       struct pci_dev *dev, int speed);
 	void		*release_data;
 	unsigned int	ignore_reset_delay:1;	/* For entire hierarchy */
 	unsigned int	no_ext_tags:1;		/* No Extended Tags */

-- 
2.34.1