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Date: Thu, 9 May 2024 12:39:34 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: <linux-pci@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, "Lorenzo
Pieralisi" <lorenzo.pieralisi@....com>, Rob Herring <robh@...nel.org>,
Krzysztof Wilczyński <kw@...ux.com>, Lukas Wunner
<lukas@...ner.de>, Alexandru Gagniuc <mr.nuke.me@...il.com>, "Krishna
chaitanya chundru" <quic_krichai@...cinc.com>, Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com>, "Rafael J. Wysocki"
<rafael@...nel.org>, <linux-pm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>,
Amit Kucheria <amitk@...nel.org>, Zhang Rui <rui.zhang@...el.com>, Christophe
JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v5 5/8] PCI/bwctrl: Re-add BW notification portdrv as
PCIe BW controller
On Wed, 8 May 2024 16:47:41 +0300
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:
> This mostly reverts the commit b4c7d2076b4e ("PCI/LINK: Remove
> bandwidth notification"). An upcoming commit extends this driver
> building PCIe bandwidth controller on top of it.
>
> The PCIe bandwidth notification were first added in the commit
> e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth
> notification") but later had to be removed. The significant changes
> compared with the old bandwidth notification driver include:
>
> 1) Don't print the notifications into kernel log, just keep the Link
> Speed cached into the struct pci_bus updated. While somewhat
> unfortunate, the log spam was the source of complaints that
> eventually lead to the removal of the bandwidth notifications driver
> (see the links below for further information).
>
> 2) Besides the Link Bandwidth Management Interrupt, enable also Link
> Autonomous Bandwidth Interrupt to cover the other source of
> bandwidth changes.
>
> 3) Use threaded IRQ with IRQF_ONESHOT to handle Bandwidth Notification
> Interrupts to address the problem fixed in the commit 3e82a7f9031f
> ("PCI/LINK: Supply IRQ handler so level-triggered IRQs are acked")).
>
> 4) Handle Link Speed updates robustly. Refresh the cached Link Speed
> when enabling Bandwidth Notification Interrupts, and solve the race
> between Link Speed read and LBMS/LABS update in
> pcie_bwnotif_irq_thread().
>
> 5) Use concurrency safe LNKCTL RMW operations.
>
> 6) The driver is now called PCIe bwctrl (bandwidth controller) instead
> of just bandwidth notifications because of increased scope and
> functionality within the driver.
>
> 7) Coexist with the Target Link Speed quirk in
> pcie_failed_link_retrain(). Provide LBMS counting API for it.
>
> 8) Tweaks to variable/functions names for consistency and length
> reasons.
>
> Bandwidth Notifications enable the cur_bus_speed in the struct pci_bus
> to keep track PCIe Link Speed changes.
>
> Link: https://lore.kernel.org/all/20190429185611.121751-1-helgaas@kernel.org/
> Link: https://lore.kernel.org/linux-pci/20190501142942.26972-1-keith.busch@intel.com/
> Link: https://lore.kernel.org/linux-pci/20200115221008.GA191037@google.com/
> Suggested-by: Lukas Wunner <lukas@...ner.de> # Building bwctrl on top of bwnotif
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
A few trivial things inline. Either way LGTM
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
> index 6461aa93fe76..6357bc219632 100644
> --- a/drivers/pci/pcie/Makefile
> +++ b/drivers/pci/pcie/Makefile
> @@ -12,4 +12,5 @@ obj-$(CONFIG_PCIEAER_INJECT) += aer_inject.o
> obj-$(CONFIG_PCIE_PME) += pme.o
> obj-$(CONFIG_PCIE_DPC) += dpc.o
> obj-$(CONFIG_PCIE_PTM) += ptm.o
> +obj-$(CONFIG_PCIE_BWCTRL) += bwctrl.o
> obj-$(CONFIG_PCIE_EDR) += edr.o
> diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
> new file mode 100644
> index 000000000000..5afc533dd0a9
> --- /dev/null
> +++ b/drivers/pci/pcie/bwctrl.c
> @@ -0,0 +1,185 @@
> +
> +static irqreturn_t pcie_bwnotif_irq_thread(int irq, void *context)
> +{
> + struct pcie_device *srv = context;
> + struct pcie_bwctrl_data *data = get_service_data(srv);
> + struct pci_dev *port = srv->port;
> + u16 link_status, events;
> + int ret;
> +
> + ret = pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
> + events = link_status & (PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_LABS);
> +
> + if (ret != PCIBIOS_SUCCESSFUL || !events)
> + return IRQ_NONE;
Trivial, but nicer to not use link_status if it is garbage (even briefly)
Only a couple of lines more to keep it clean.
ret = pcie...
if (ret != PCI_BIOS_SUCCESSFUL)
return IRQ_NONE;
events = ...
if (!events)
return IRQ_NONE;
> +
> + if (events & PCI_EXP_LNKSTA_LBMS)
> + atomic_inc(&data->lbms_count);
> +
> + pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
> +
> + /*
> + * Interrupts will not be triggered from any further Link Speed
> + * change until LBMS is cleared by the write. Therefore, re-read the
> + * speed (inside pcie_update_link_speed()) after LBMS has been
> + * cleared to avoid missing link speed changes.
> + */
> + pcie_update_link_speed(port->subordinate);
> +
> + return IRQ_HANDLED;
> +}
> +
> +static int pcie_bwnotif_probe(struct pcie_device *srv)
> +{
> + struct pci_dev *port = srv->port;
> + int ret;
> +
> + struct pcie_bwctrl_data *data __free(kfree) =
> + kzalloc(sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + set_service_data(srv, data);
> +
> + ret = request_threaded_irq(srv->irq, NULL, pcie_bwnotif_irq_thread,
> + IRQF_SHARED | IRQF_ONESHOT, "PCIe bwctrl", srv);
> + if (ret)
> + return ret;
> +
> + port->link_bwctrl = no_free_ptr(data);
> + pcie_bwnotif_enable(srv);
> + pci_info(port, "enabled with IRQ %d\n", srv->irq);
Rather noisy given this is easy enough to establish via other paths.
pci_dbg() maybe?
> +
> + return 0;
> +}
> +
> +static void pcie_bwnotif_remove(struct pcie_device *srv)
> +{
> + struct pcie_bwctrl_data *data = get_service_data(srv);
> +
> + scoped_guard(rwsem_write, &pcie_bwctrl_remove_rwsem)
> + srv->port->link_bwctrl = NULL;
> +
> + pcie_bwnotif_disable(srv->port);
Trivial but I'd like a comment to say why this needs to be done after
the link_bwctrl = NULL above (or if not, move it before that.
That puts the tear down slightly out of order vs set up.
> + free_irq(srv->irq, srv);
> + kfree(data);
> +}
> +
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