On Mon, 19 May 2025, Krishna Chaitanya Chundru wrote:
> 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. 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@xxxxxxxxxxxxxxxx>
> ---
> drivers/pci/pcie/bwctrl.c | 15 +++++++++++++++
> include/linux/pci.h | 14 ++++++++++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
> index d8d2aa85a22928b99c5bba1d2bcc5647c0edeeb6..3525bc0cd10f1dd7794abbe84ccb10e2c53a10af 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_rootbus = 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 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_scale_bus_bw) {
> + ret = host->pre_scale_bus_bw(host, port, 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 (bus && is_rootbus && host->post_scale_bus_bw)
> + host->post_scale_bus_bw(host, port, pci_bus_speed2lnkctl2(bus->cur_bus_speed));
> +
> return ret;
> }
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 51e2bd6405cda5acc33d268bbe1d491b145e083f..7eb0856ba0ed20bd1336683b68add124c7483902 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -601,6 +601,20 @@ 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
BW
> + * 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
Root Port
> + * client endpoint driver, so there is no need for explicit locking mechanisms.
Endpoint
> + */
> + int (*pre_scale_bus_bw)(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.
> + */
Please fold comments to 80 characters.
> + void (*post_scale_bus_bw)(struct pci_host_bridge *bridge, struct pci_dev *dev, int speed);
I still don't like the names. Maybe simply pre/post_link_speed_change
would sound more generic.
Not a show-stopper but the current name sounds pretty esoteric.
> void *release_data;
> unsigned int ignore_reset_delay:1; /* For entire hierarchy */
> unsigned int no_ext_tags:1; /* No Extended Tags */
>
>
--
i.
