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

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Date:   Mon, 27 Feb 2017 19:13:07 +0000
From:   "Chalamarla, Tirumalesh" <Tirumalesh.Chalamarla@...ium.com>
To:     David Daney <ddaney.cavm@...il.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Jaggi, Manish" <Manish.Jaggi@...ium.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Richter, Robert" <Robert.Richter@...ium.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH] PCI: Add cavium acs pci quirk



On 2/27/17, 11:02 AM, "David Daney" <ddaney.cavm@...il.com> wrote:

    On 02/14/2017 07:07 AM, Bjorn Helgaas wrote:
    > On Mon, Feb 13, 2017 at 09:44:57PM -0700, Alex Williamson wrote:
    >> 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,
    >
    > I'd be happy to revert this, but it would be easier if somebody sent a
    > patch and a changelog.
    >
    
    I agree that it should be reverted.
    
    I was hoping that Manish or Tirumalesh would fix this properly by only 
    activating the quirk on the faulty hardware, but such a fix has never 
    appeared.

This was supposed to be true for all Cavium chips. We got such answer from Hardware architects, but it might change in the future. 
I will be happy to replace this with DEVICE_ID.
Manish,
Could you please take this u, if not I will send a patch to do this.

Tirumalesh. 
    
    David Daney