linux-kernel - Re: [PATCH] PCI: Add cavium acs pci quirk

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Date:   Mon, 13 Feb 2017 21:44:57 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Manish Jaggi <mjaggi@...iumnetworks.com>
Cc:     <linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        Tirumalesh Chalamarla <tchalamarla@...ium.com>,
        "Richter, Robert" <Robert.Richter@...iumnetworks.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI: Add cavium acs pci quirk

On Sat, 30 Jan 2016 01:33:58 +0530
Manish Jaggi <mjaggi@...iumnetworks.com> wrote:

> Cavium devices matching this quirk do not perform
> peer-to-peer with other functions, allowing masking out
> these bits as if they were unimplemented in the ACS capability.
> 
> Acked-by: Tirumalesh Chalamarla <tchalamarla@...ium.com>
> Signed-off-by: Manish Jaggi <mjaggi@...iumnetworks.com>
> ---
>  drivers/pci/quirks.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 7e32730..a300fa6 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -3814,6 +3814,19 @@ static int pci_quirk_amd_sb_acs(struct pci_dev *dev, u16 acs_flags)
>  #endif
>  }
> 
> +static int pci_quirk_cavium_acs(struct pci_dev *dev, u16 acs_flags)
> +{
> +	/*
> +	 * Cavium devices matching this quirk do not perform
> +	 * peer-to-peer with other functions, allowing masking out
> +	 * these bits as if they were unimplemented in the ACS capability.
> +	 */
> +	acs_flags &= ~(PCI_ACS_SV | PCI_ACS_TB | PCI_ACS_RR |
> +		       PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_DT);
> +
> +	return acs_flags ? 0 : 1;
> +}
> +
>  /*
>   * Many Intel PCH root ports do provide ACS-like features to disable peer
>   * transactions and validate bus numbers in requests, but do not provide an
> @@ -3966,6 +3979,8 @@ static const struct pci_dev_acs_enabled {
>  	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID, pci_quirk_intel_pch_acs },
>  	{ 0x19a2, 0x710, pci_quirk_mf_endpoint_acs }, /* Emulex BE3-R */
>  	{ 0x10df, 0x720, pci_quirk_mf_endpoint_acs }, /* Emulex Skyhawk-R */
> +	/* Cavium ThunderX */
> +	{ PCI_VENDOR_ID_CAVIUM, PCI_ANY_ID, pci_quirk_cavium_acs },
>  	{ 0 }
>  };
> 

Apologies for not catching this, but what sort of crystal ball do you
have that can predict not only current devices, but future devices will
not support peer-to-peer features?  Is there an internal design
guidelines reference specification for Cavium that we can realistically
expect this to remain consistent, or is this just an attempt to never
think about ACS again at the customer's peril?  What about the existing
non-ThunderX products with Cavium vendor ID, does this really apply to
those?  I would strongly suggest taking the device ID into account.
See examples like the pci_quirk_intel_pch_acs quirk where the initial
filter is PCI_ANY_ID, but specific device types and ranges of device
IDs are identified by the function for evaluation.  This seems reckless
to me and I'd advise that it be reverted.  Thanks,

Alex