linux-kernel - Re: [PATCH v5 3/3] PCI: Introduce the disable_acs

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Date:   Tue, 10 Jul 2018 13:19:15 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-doc@...r.kernel.org, Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian König <christian.koenig@....com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v5 3/3] PCI: Introduce the disable_acs_redir parameter

On Mon, 9 Jul 2018 16:27:40 -0600
Logan Gunthorpe <logang@...tatee.com> wrote:

> Hey Alex,
> 
> On 06/07/18 04:56 PM, Alex Williamson wrote:
> > Maybe we track if we enabled ACS via a device specific quirk and
> > minimally print an incompatibility error if it's also specified for
> > disable_acs_redir?  Thanks,  
> 
> Ok, I dug into this a bit and I think tracking if we enabled via a
> device specific quirk does not work. If 'pci_acs_enable' is not set, we
> wouldn't know if we used a device specific quirk and still try to
> disable a quirked device the standard way.
> 
> Instead, I've looked at adding a device specific disable_acs_redir
> function next to enable_acs. In this way, the device specific quirks can
> override the operation. See the diff below.
> 
> Implementing the Intel SPT PCH version is pretty trivial, so I've done
> that. The Intel PCH variant I've just left as unsupported and printed a
> warning.
> 
> If this sounds good to you, I'll fold it into my patchset and resubmit a v6.
> 
> Thanks,
> 
> Logan
> 
> --
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 079f7c911e09..54001b307496 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3028,6 +3028,9 @@ static void pci_disable_acs_redir(struct pci_dev *dev)
>  	if (!pos)
>  		return;
> 
> +	if (!pci_dev_specific_disable_acs_redir(dev))
> +		return;
> +
>  	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
> 
>  	/* P2P Request & Completion Redirect */
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index f439de848658..c976a025ae92 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -4526,6 +4526,16 @@ static int pci_quirk_enable_intel_pch_acs(struct
> pci_dev *dev)
>  	return 0;
>  }
> 
> +static int pci_quirk_disable_intel_pch_acs_redir(struct pci_dev *dev)
> +{
> +	if (!pci_quirk_intel_pch_acs_match(dev))
> +		return -ENOTTY;
> +
> +	pci_warn(dev, "Disabling ACS redirect on the Intel PCH root port is
> not supported\n");
> +
> +	return 0;
> +}

Note that these devices don't have an ACS capability, so they should
drop out just as any other device without an ACS capability would.
Should pci_disable_acs_redir() perhaps issue the pci_warn() for all
such devices, removing this device specific disable function?

> +
>  static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
>  {
>  	int pos;
> @@ -4553,22 +4563,53 @@ static int
> pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
>  	return 0;
>  }
> 
> -static const struct pci_dev_enable_acs {
> +static int pci_quirk_disable_intel_spt_pch_acs_redir(struct pci_dev *dev)
> +{
> +	int pos;
> +	u32 cap, ctrl;
> +
> +	if (!pci_quirk_intel_spt_pch_acs_match(dev))
> +		return -ENOTTY;
> +
> +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
> +	if (!pos)
> +		return -ENOTTY;
> +
> +	pci_read_config_dword(dev, pos + PCI_ACS_CAP, &cap);
> +	pci_read_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, &ctrl);
> +
> +	ctrl &= ~(PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC);
> +
> +	pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);
> +
> +	pci_info(dev, "Intel SPT PCH root port workaround: disabled ACS
> redirect\n");
> +
> +	return 0;
> +}
> +
> +static const struct pci_dev_acs_ops {
>  	u16 vendor;
>  	u16 device;
>  	int (*enable_acs)(struct pci_dev *dev);
> -} pci_dev_enable_acs[] = {
> -	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID, pci_quirk_enable_intel_pch_acs },
> -	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID, pci_quirk_enable_intel_spt_pch_acs },
> +	int (*disable_acs_redir)(struct pci_dev *dev);
> +} pci_dev_acs_ops[] = {
> +	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
> +	  .enable_acs = pci_quirk_enable_intel_pch_acs,
> +	  .disable_acs_redir = pci_quirk_disable_intel_pch_acs_redir,
> +	},
> +	{ PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
> +	  .enable_acs = pci_quirk_enable_intel_spt_pch_acs,
> +	  .disable_acs_redir = pci_quirk_disable_intel_spt_pch_acs_redir
> +	},

Kind of cumbersome, and as above, maybe the reverse path is optional.
I wonder if there's a better callback we should use or if we should not
rely on quirks providing both.

>  	{ 0 }
>  };
> 
>  int pci_dev_specific_enable_acs(struct pci_dev *dev)
>  {
> -	const struct pci_dev_enable_acs *i;
> +	const struct pci_dev_acs_ops *i;
>  	int ret;
> 
> -	for (i = pci_dev_enable_acs; i->enable_acs; i++) {
> +	for (i = pci_dev_acs_ops; i->enable_acs; i++) {

Perhaps this would walk via ARRAY_SIZE if we decide one or the other
callback is optional.

>  		if ((i->vendor == dev->vendor ||
>  		     i->vendor == (u16)PCI_ANY_ID) &&
>  		    (i->device == dev->device ||
> @@ -4582,6 +4623,25 @@ int pci_dev_specific_enable_acs(struct pci_dev *dev)
>  	return -ENOTTY;
>  }
> 
> +int pci_dev_specific_disable_acs_redir(struct pci_dev *dev)
> +{
> +	const struct pci_dev_acs_ops *i;
> +	int ret;
> +
> +	for (i = pci_dev_acs_ops; i->enable_acs; i++) {

Test i->disable_acs_redir?

> +		if ((i->vendor == dev->vendor ||
> +		     i->vendor == (u16)PCI_ANY_ID) &&
> +		    (i->device == dev->device ||
> +		     i->device == (u16)PCI_ANY_ID)) {
> +			ret = i->disable_acs_redir(dev);
> +			if (ret >= 0)
> +				return ret;
> +		}
> +	}
> +
> +	return -ENOTTY;
> +}
> +
>  /*
>   * The PCI capabilities list for Intel DH895xCC VFs (device ID 0x0443) with
>   * QuickAssist Technology (QAT) is prematurely terminated in hardware.  The
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 340029b2fb38..7ee208aa1a31 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1878,6 +1878,7 @@ enum pci_fixup_pass {
>  void pci_fixup_device(enum pci_fixup_pass pass, struct pci_dev *dev);
>  int pci_dev_specific_acs_enabled(struct pci_dev *dev, u16 acs_flags);
>  int pci_dev_specific_enable_acs(struct pci_dev *dev);
> +int pci_dev_specific_disable_acs_redir(struct pci_dev *dev);

static inline version for !CONFIG_PCI_QUIRKS?  Thanks,

Alex

>  #else
>  static inline void pci_fixup_device(enum pci_fixup_pass pass,
>  				    struct pci_dev *dev) { }