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Message-ID: <20250423210454.GA455057@bhelgaas>
Date: Wed, 23 Apr 2025 16:04:54 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Lukas Wunner <lukas@...ner.de>, Bjorn Helgaas <bhelgaas@...gle.com>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] PCI/bwctrl: Replace lbms_count with
PCI_LINK_LBMS_SEEN flag
On Tue, Apr 22, 2025 at 02:55:47PM +0300, Ilpo Järvinen wrote:
> PCIe BW controller counts LBMS assertions for the purposes of the
> Target Speed quirk. It was also a plan to expose the LBMS count through
> sysfs to allow better diagnosing link related issues. Lukas Wunner
> suggested, however, that adding a trace event would be better for
> diagnostics purposes. Leaving only Target Speed quirk as an user of the
> lbms_count.
>
> The logic in the Target Speed quirk does not require keeping count of
> LBMS assertions but a simple flag is enough which can be placed into
> pci_dev's priv_flags. The reduced complexity allows removing
> pcie_bwctrl_lbms_rwsem.
>
> As bwctrl is not yet probed when the Target Speed quirk runs during
> boot, the LBMS in Link Status register has to still be checked by
> the quirk.
>
> The priv_flags numbering is not continuous because hotplug code added
> a few flags to fill numbers 4-5 (hotplug and bwctrl changes are routed
> through in different branches).
>
> Suggested-by: Lukas Wunner <lukas@...ner.de>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>
> This will conflict with the new flags Lukas added due to the hp fixes
> but it should be simple to deal with that conflict while merging the
> topic branches.
>
> v2:
> - Change flag value to 6 to make merging with the newly added HP flags easier
> - Renamed flag to PCI_LINK_LBMS_SEEN to match the naming of the new HP flags
>
> drivers/pci/hotplug/pciehp_ctrl.c | 2 +-
> drivers/pci/pci.c | 2 +-
> drivers/pci/pci.h | 10 ++---
> drivers/pci/pcie/bwctrl.c | 63 +++++++++----------------------
> drivers/pci/quirks.c | 10 ++---
> 5 files changed, 25 insertions(+), 62 deletions(-)
Applied to pci/bwctrl for v6.16, on the assumption that everybody's
happy with this. Thanks!
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index d603a7aa7483..bcc938d4420f 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -131,7 +131,7 @@ static void remove_board(struct controller *ctrl, bool safe_removal)
> INDICATOR_NOOP);
>
> /* Don't carry LBMS indications across */
> - pcie_reset_lbms_count(ctrl->pcie->port);
> + pcie_reset_lbms(ctrl->pcie->port);
> }
>
> static int pciehp_enable_slot(struct controller *ctrl);
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 4d7c9f64ea24..3d94cf33c1b6 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4757,7 +4757,7 @@ int pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
> * to track link speed or width changes made by hardware itself
> * in attempt to correct unreliable link operation.
> */
> - pcie_reset_lbms_count(pdev);
> + pcie_reset_lbms(pdev);
> return rc;
> }
>
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index b81e99cd4b62..887811fbe722 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -557,6 +557,7 @@ static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
> #define PCI_DPC_RECOVERED 1
> #define PCI_DPC_RECOVERING 2
> #define PCI_DEV_REMOVED 3
> +#define PCI_LINK_LBMS_SEEN 6
>
> static inline void pci_dev_assign_added(struct pci_dev *dev)
> {
> @@ -824,14 +825,9 @@ static inline void pcie_ecrc_get_policy(char *str) { }
> #endif
>
> #ifdef CONFIG_PCIEPORTBUS
> -void pcie_reset_lbms_count(struct pci_dev *port);
> -int pcie_lbms_count(struct pci_dev *port, unsigned long *val);
> +void pcie_reset_lbms(struct pci_dev *port);
> #else
> -static inline void pcie_reset_lbms_count(struct pci_dev *port) {}
> -static inline int pcie_lbms_count(struct pci_dev *port, unsigned long *val)
> -{
> - return -EOPNOTSUPP;
> -}
> +static inline void pcie_reset_lbms(struct pci_dev *port) {}
> #endif
>
> struct pci_dev_reset_methods {
> diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
> index d8d2aa85a229..ab0387ff2de2 100644
> --- a/drivers/pci/pcie/bwctrl.c
> +++ b/drivers/pci/pcie/bwctrl.c
> @@ -38,12 +38,10 @@
> /**
> * struct pcie_bwctrl_data - PCIe bandwidth controller
> * @set_speed_mutex: Serializes link speed changes
> - * @lbms_count: Count for LBMS (since last reset)
> * @cdev: Thermal cooling device associated with the port
> */
> struct pcie_bwctrl_data {
> struct mutex set_speed_mutex;
> - atomic_t lbms_count;
> struct thermal_cooling_device *cdev;
> };
>
> @@ -202,15 +200,14 @@ int pcie_set_target_speed(struct pci_dev *port, enum pci_bus_speed speed_req,
>
> static void pcie_bwnotif_enable(struct pcie_device *srv)
> {
> - struct pcie_bwctrl_data *data = srv->port->link_bwctrl;
> struct pci_dev *port = srv->port;
> u16 link_status;
> int ret;
>
> - /* Count LBMS seen so far as one */
> + /* Note down if LBMS has been seen so far */
> ret = pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
> if (ret == PCIBIOS_SUCCESSFUL && link_status & PCI_EXP_LNKSTA_LBMS)
> - atomic_inc(&data->lbms_count);
> + set_bit(PCI_LINK_LBMS_SEEN, &port->priv_flags);
>
> pcie_capability_set_word(port, PCI_EXP_LNKCTL,
> PCI_EXP_LNKCTL_LBMIE | PCI_EXP_LNKCTL_LABIE);
> @@ -233,7 +230,6 @@ static void pcie_bwnotif_disable(struct pci_dev *port)
> static irqreturn_t pcie_bwnotif_irq(int irq, void *context)
> {
> struct pcie_device *srv = context;
> - struct pcie_bwctrl_data *data = srv->port->link_bwctrl;
> struct pci_dev *port = srv->port;
> u16 link_status, events;
> int ret;
> @@ -247,7 +243,7 @@ static irqreturn_t pcie_bwnotif_irq(int irq, void *context)
> return IRQ_NONE;
>
> if (events & PCI_EXP_LNKSTA_LBMS)
> - atomic_inc(&data->lbms_count);
> + set_bit(PCI_LINK_LBMS_SEEN, &port->priv_flags);
>
> pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
>
> @@ -262,31 +258,10 @@ static irqreturn_t pcie_bwnotif_irq(int irq, void *context)
> return IRQ_HANDLED;
> }
>
> -void pcie_reset_lbms_count(struct pci_dev *port)
> +void pcie_reset_lbms(struct pci_dev *port)
> {
> - struct pcie_bwctrl_data *data;
> -
> - guard(rwsem_read)(&pcie_bwctrl_lbms_rwsem);
> - data = port->link_bwctrl;
> - if (data)
> - atomic_set(&data->lbms_count, 0);
> - else
> - pcie_capability_write_word(port, PCI_EXP_LNKSTA,
> - PCI_EXP_LNKSTA_LBMS);
> -}
> -
> -int pcie_lbms_count(struct pci_dev *port, unsigned long *val)
> -{
> - struct pcie_bwctrl_data *data;
> -
> - guard(rwsem_read)(&pcie_bwctrl_lbms_rwsem);
> - data = port->link_bwctrl;
> - if (!data)
> - return -ENOTTY;
> -
> - *val = atomic_read(&data->lbms_count);
> -
> - return 0;
> + clear_bit(PCI_LINK_LBMS_SEEN, &port->priv_flags);
> + pcie_capability_write_word(port, PCI_EXP_LNKSTA, PCI_EXP_LNKSTA_LBMS);
> }
>
> static int pcie_bwnotif_probe(struct pcie_device *srv)
> @@ -308,18 +283,16 @@ static int pcie_bwnotif_probe(struct pcie_device *srv)
> return ret;
>
> scoped_guard(rwsem_write, &pcie_bwctrl_setspeed_rwsem) {
> - scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem) {
> - port->link_bwctrl = data;
> + port->link_bwctrl = data;
>
> - ret = request_irq(srv->irq, pcie_bwnotif_irq,
> - IRQF_SHARED, "PCIe bwctrl", srv);
> - if (ret) {
> - port->link_bwctrl = NULL;
> - return ret;
> - }
> -
> - pcie_bwnotif_enable(srv);
> + ret = request_irq(srv->irq, pcie_bwnotif_irq,
> + IRQF_SHARED, "PCIe bwctrl", srv);
> + if (ret) {
> + port->link_bwctrl = NULL;
> + return ret;
> }
> +
> + pcie_bwnotif_enable(srv);
> }
>
> pci_dbg(port, "enabled with IRQ %d\n", srv->irq);
> @@ -339,13 +312,11 @@ static void pcie_bwnotif_remove(struct pcie_device *srv)
> pcie_cooling_device_unregister(data->cdev);
>
> scoped_guard(rwsem_write, &pcie_bwctrl_setspeed_rwsem) {
> - scoped_guard(rwsem_write, &pcie_bwctrl_lbms_rwsem) {
> - pcie_bwnotif_disable(srv->port);
> + pcie_bwnotif_disable(srv->port);
>
> - free_irq(srv->irq, srv);
> + free_irq(srv->irq, srv);
>
> - srv->port->link_bwctrl = NULL;
> - }
> + srv->port->link_bwctrl = NULL;
> }
> }
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 8d610c17e0f2..64ac1ee944d3 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -38,14 +38,10 @@
>
> static bool pcie_lbms_seen(struct pci_dev *dev, u16 lnksta)
> {
> - unsigned long count;
> - int ret;
> -
> - ret = pcie_lbms_count(dev, &count);
> - if (ret < 0)
> - return lnksta & PCI_EXP_LNKSTA_LBMS;
> + if (test_bit(PCI_LINK_LBMS_SEEN, &dev->priv_flags))
> + return true;
>
> - return count > 0;
> + return lnksta & PCI_EXP_LNKSTA_LBMS;
> }
>
> /*
>
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> --
> 2.39.5
>
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