linux-kernel - Re: [PATCH v5 6/8] PCI/bwctrl: Add API to set PCIe Link Speed

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Date: Thu, 9 May 2024 12:53:58 +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 6/8] PCI/bwctrl: Add API to set PCIe Link Speed

On Wed,  8 May 2024 16:47:42 +0300
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> Currently, PCIe Link Speeds are adjusted by custom code rather than in
> a common function provided in PCI core. PCIe bandwidth controller
> (bwctrl) introduces an in-kernel API to set PCIe Link Speed. Convert
> Target Speed quirk to use the new API.
> 
> The new API is also intended to be used in an upcoming commit that adds
> a thermal cooling device to throttle PCIe bandwidth when thermal
> thresholds are reached.
> 
> The PCIe bandwidth control procedure is as follows. The highest speed
> supported by the Port and the PCIe device which is not higher than the
> requested speed is selected and written into the Target Link Speed in
> the Link Control 2 Register. Then bandwidth controller retrains the
> PCIe Link.
> 
> Bandwidth Notifications enable the cur_bus_speed in the struct pci_bus
> to keep track PCIe Link Speed changes. While Bandwidth Notifications
> should also be generated when bandwidth controller alters the PCIe Link
> Speed, a few platforms do not deliver LMBS interrupt after Link
> Training as expected. Thus, after changing the Link Speed, bandwidth
> controller makes additional read for the Link Status Register to ensure
> cur_bus_speed is consistent with the new PCIe Link Speed.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> ---
>  drivers/pci/pci.h         |  13 ++++
>  drivers/pci/pcie/Makefile |   2 +-
>  drivers/pci/pcie/bwctrl.c | 147 ++++++++++++++++++++++++++++++++++++++
>  drivers/pci/quirks.c      |  12 +---
>  include/linux/pci.h       |   3 +
>  5 files changed, 166 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 416540baf27b..324899fbad0a 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -270,6 +270,19 @@ void pci_disable_bridge_window(struct pci_dev *dev);
>  struct pci_bus *pci_bus_get(struct pci_bus *bus);
>  void pci_bus_put(struct pci_bus *bus);
>  
> +#define PCIE_LNKCAP_SLS2SPEED(lnkcap)					\
> +({									\
> +	u32 _lnkcap = (lnkcap) & PCI_EXP_LNKCAP_SLS;			\

Why the inconsistency wrt to PCIE_LNKCAP2_SLS2SPEED which doesn't bother with
this initial mask. It's not needed afterall as the bits checked are all in the
mask anyway?

I don't really mind which form but they should look the same.

> +									\
> +	(_lnkcap == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT :	\
> +	 _lnkcap == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT :	\
> +	 _lnkcap == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT :	\
> +	 _lnkcap == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT :	\
> +	 _lnkcap == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT :	\
> +	 _lnkcap == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT :	\
> +	 PCI_SPEED_UNKNOWN);						\
> +})
> +