linux-kernel - Re: [PATCH v2 RESEND 1/1] PCI: pcie_bus

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Message-ID: <CA+-6iNwWtJTOdj2Fw-AgjVFRFAZrZ+vvTCOmMEiiYHvbcrap+w@mail.gmail.com>
Date:   Wed, 30 Sep 2020 16:57:47 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 RESEND 1/1] PCI: pcie_bus_config can be set at build time

On Tue, Sep 29, 2020 at 5:31 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Mon, Sep 28, 2020 at 03:46:51PM -0400, Jim Quinlan wrote:
> > The Kconfig is modified so that the pcie_bus_config setting can be done at
> > build time in the same manner as the CONFIG_PCIEASPM_XXXX choice.  The
> > pci_bus_config setting may still be overridden by the bootline param.
> >
> > Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
>
> Applied to pci/enumeration for v5.10, thanks!
>
> I tweaked the help texts and made the Kconfig stuff depend on
> CONFIG_EXPERT.  Will that still be enough for what you need?  I'm
> worried that users will get themselves in trouble if they fiddle with
> things without really understanding what's going on.

Hi Bjorn,

I didn't even know about CONFIG_EXPERT -- makes sense and looks good to me!

Thanks much,
Jim Quinlan
Broadcom STB

>
> Here's what I applied:
>
>
> commit 2a87f534d198 ("PCI: Add Kconfig options for pcie_bus_config")
> Author: Jim Quinlan <james.quinlan@...adcom.com>
> Date:   Mon Sep 28 15:46:51 2020 -0400
>
>     PCI: Add Kconfig options for pcie_bus_config
>
>     Add Kconfig options for changing the default pcie_bus_config in the same
>     manner as the CONFIG_PCIEASPM_XXXX choice.  The pci_bus_config setting may
>     still be overridden by kernel command-line parameters, e.g.,
>     "pci=pcie_bus_tune_off".
>
>     [bhelgaas: depend on EXPERT, tweak help texts]
>     Link: https://lore.kernel.org/r/20200928194651.5393-2-james.quinlan@broadcom.com
>     Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 4bef5c2bae9f..d323b25ae27e 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -187,6 +187,68 @@ config PCI_HYPERV
>           The PCI device frontend driver allows the kernel to import arbitrary
>           PCI devices from a PCI backend to support PCI driver domains.
>
> +choice
> +       prompt "PCI Express hierarchy optimization setting"
> +       default PCIE_BUS_DEFAULT
> +       depends on PCI && EXPERT
> +       help
> +         MPS (Max Payload Size) and MRRS (Max Read Request Size) are PCIe
> +         device parameters that affect performance and the ability to
> +         support hotplug and peer-to-peer DMA.
> +
> +         The following choices set the MPS and MRRS optimization strategy
> +         at compile-time.  The choices are the same as those offered for
> +         the kernel command-line parameter 'pci', i.e.,
> +         'pci=pcie_bus_tune_off', 'pci=pcie_bus_safe',
> +         'pci=pcie_bus_perf', and 'pci=pcie_bus_peer2peer'.
> +
> +         This is a compile-time setting and can be overridden by the above
> +         command-line parameters.  If unsure, choose PCIE_BUS_DEFAULT.
> +
> +config PCIE_BUS_TUNE_OFF
> +       bool "Tune Off"
> +       depends on PCI
> +       help
> +         Use the BIOS defaults; don't touch MPS at all.  This is the same
> +         as booting with 'pci=pcie_bus_tune_off'.
> +
> +config PCIE_BUS_DEFAULT
> +       bool "Default"
> +       depends on PCI
> +       help
> +         Default choice; ensure that the MPS matches upstream bridge.
> +
> +config PCIE_BUS_SAFE
> +       bool "Safe"
> +       depends on PCI
> +       help
> +         Use largest MPS that boot-time devices support.  If you have a
> +         closed system with no possibility of adding new devices, this
> +         will use the largest MPS that's supported by all devices.  This
> +         is the same as booting with 'pci=pcie_bus_safe'.
> +
> +config PCIE_BUS_PERFORMANCE
> +       bool "Performance"
> +       depends on PCI
> +       help
> +         Use MPS and MRRS for best performance.  Ensure that a given
> +         device's MPS is no larger than its parent MPS, which allows us to
> +         keep all switches/bridges to the max MPS supported by their
> +         parent.  This is the same as booting with 'pci=pcie_bus_perf'.
> +
> +config PCIE_BUS_PEER2PEER
> +       bool "Peer2peer"
> +       depends on PCI
> +       help
> +         Set MPS = 128 for all devices.  MPS configuration effected by the
> +         other options could cause the MPS on one root port to be
> +         different than that of the MPS on another, which may cause
> +         hot-added devices or peer-to-peer DMA to fail.  Set MPS to the
> +         smallest possible value (128B) system-wide to avoid these issues.
> +         This is the same as booting with 'pci=pcie_bus_peer2peer'.
> +
> +endchoice
> +
>  source "drivers/pci/hotplug/Kconfig"
>  source "drivers/pci/controller/Kconfig"
>  source "drivers/pci/endpoint/Kconfig"
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index a458c46d7e39..49b66ba7c874 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -101,7 +101,19 @@ unsigned long pci_hotplug_mmio_pref_size = DEFAULT_HOTPLUG_MMIO_PREF_SIZE;
>  #define DEFAULT_HOTPLUG_BUS_SIZE       1
>  unsigned long pci_hotplug_bus_size = DEFAULT_HOTPLUG_BUS_SIZE;
>
> +
> +/* PCIE bus config, can be overridden by bootline param */
> +#ifdef CONFIG_PCIE_BUS_TUNE_OFF
> +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_TUNE_OFF;
> +#elif defined CONFIG_PCIE_BUS_SAFE
> +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_SAFE;
> +#elif defined CONFIG_PCIE_BUS_PERFORMANCE
> +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PERFORMANCE;
> +#elif defined CONFIG_PCIE_BUS_PEER2PEER
> +enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PEER2PEER;
> +#else
>  enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;
> +#endif
>
>  /*
>   * The default CLS is used if arch didn't set CLS explicitly and not

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