netdev - Re: [RFC PATCH net-next 04/12] PCI: Add no PM reset quirk for NVIDIA Spectrum devices

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Date: Wed, 18 Oct 2023 14:40:41 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ido Schimmel <idosch@...dia.com>
Cc: netdev@...r.kernel.org, linux-pci@...r.kernel.org, davem@...emloft.net,
	kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com,
	bhelgaas@...gle.com, alex.williamson@...hat.com, lukas@...ner.de,
	petrm@...dia.com, jiri@...dia.com, mlxsw@...dia.com
Subject: Re: [RFC PATCH net-next 04/12] PCI: Add no PM reset quirk for NVIDIA
 Spectrum devices

On Tue, Oct 17, 2023 at 10:42:49AM +0300, Ido Schimmel wrote:
> Spectrum-{1,2,3,4} devices report that a D3hot->D0 transition causes a
> reset (i.e., they advertise NoSoftRst-). However, this transition seems
> to have no effect on the device: It continues to be operational and
> network ports remain up. Advertising this support makes it seem as if a
> PM reset is viable for these devices. Mark it as unavailable to skip it
> when testing reset methods.
> 
> Before:
> 
>  # cat /sys/bus/pci/devices/0000\:03\:00.0/reset_method
>  pm bus
> 
> After:
> 
>  # cat /sys/bus/pci/devices/0000\:03\:00.0/reset_method
>  bus
> 
> Signed-off-by: Ido Schimmel <idosch@...dia.com>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

Hopefully since these are NVIDIA parts and you work at NVIDIA, this is
stronger than "this transition *seems* to have no effect" :)

The spec actually says NoSoftRst- means internal state is "undefined"
after a D3hot->D0 transition, so preserving it would not be a defect
per spec.  The kernel assumption that NoSoftRst- means the device will
do a reset is perhaps a little too aggressive.

> ---
>  drivers/pci/quirks.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index eeec1d6f9023..23f6bd2184e2 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3784,6 +3784,19 @@ static void quirk_no_pm_reset(struct pci_dev *dev)
>  DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_ATI, PCI_ANY_ID,
>  			       PCI_CLASS_DISPLAY_VGA, 8, quirk_no_pm_reset);
>  
> +/*
> + * Spectrum-{1,2,3,4} devices report that a D3hot->D0 transition causes a reset
> + * (i.e., they advertise NoSoftRst-). However, this transition seems to have no
> + * effect on the device: It continues to be operational and network ports
> + * remain up. Advertising this support makes it seem as if a PM reset is viable
> + * for these devices. Mark it as unavailable to skip it when testing reset
> + * methods.
> + */
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MELLANOX, 0xcb84, quirk_no_pm_reset);
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MELLANOX, 0xcf6c, quirk_no_pm_reset);
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MELLANOX, 0xcf70, quirk_no_pm_reset);
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MELLANOX, 0xcf80, quirk_no_pm_reset);
> +
>  /*
>   * Thunderbolt controllers with broken MSI hotplug signaling:
>   * Entire 1st generation (Light Ridge, Eagle Ridge, Light Peak) and part
> -- 
> 2.40.1
>