linux-kernel - Re: [PATCH 1/1] Enable LTR/OBFF before device is used by driver

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Date:	Wed, 30 May 2012 12:13:14 -0400
From:	Don Dutile <ddutile@...hat.com>
To:	Xudong Hao <xudong.hao@...ux.intel.com>
CC:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, avi@...hat.com,
	alex.williamson@...hat.com, xiantao.zhang@...el.com,
	xudong.hao@...el.com
Subject: Re: [PATCH 1/1] Enable LTR/OBFF before device is used by driver

While you are making the other recommended fixes, could
you add/create a pci_obff_supported() function, like the pci_ltr_supported()
function, and more importantly, add it to the pci_disable_obff() function?
The latter does not check that DEVCAP2 is supported, and thus, could be
writing to non-existent (potentially private) cap space (i.e., a V1 CAP device,
which do exist in the marketplace).

The [enable,disable]_ltr functions do a good job of doing pci_ltr_supported()
checks, but the obff enable,disable functions should have similar calls.


On 05/13/2012 10:48 PM, Xudong Hao wrote:
> Enable LTR(Latency tolerance reporting) and OBFF(optimized buffer flush/fill) in
>   pci_enable_device(), so that they are enabled before the device is used by driver.
>
> Signed-off-by: Xudong Hao<xudong.hao@...el.com>
>
> ---
>   drivers/pci/pci.c |   29 +++++++++++++++++++++++++++++
>   1 files changed, 29 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 111569c..2369883 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1134,6 +1134,31 @@ int pci_load_and_free_saved_state(struct pci_dev *dev,
>   }
>   EXPORT_SYMBOL_GPL(pci_load_and_free_saved_state);
>
> +static void pci_enable_dev_caps(struct pci_dev *dev)
> +{
> +       /* set default value */
> +       unsigned long type = PCI_EXP_OBFF_SIGNAL_ALWAYS;
> +
> +       /* LTR(Latency tolerance reporting) allows devices to send
> +        * messages to the root complex indicating their latency
> +        * tolerance for snooped&  unsnooped memory transactions.
> +        */
> +       pci_enable_ltr(dev);
> +
> +       /* OBFF (optimized buffer flush/fill), where supported,
> +        * can help improve energy efficiency by giving devices
> +        * information about when interrupts and other activity
> +        * will have a reduced power impact.
> +        */
> +       pci_enable_obff(dev, type);
> +}
> +
> +static void pci_disable_dev_caps(struct pci_dev *dev)
> +{
> +       pci_disable_obff(dev);
> +       pci_disable_ltr(dev);
> +}
> +
>   static int do_pci_enable_device(struct pci_dev *dev, int bars)
>   {
>          int err;
> @@ -1146,6 +1171,9 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars)
>                  return err;
>          pci_fixup_device(pci_fixup_enable, dev);
>
> +       /* Enable some device capibility before it's used by driver. */
> +       pci_enable_dev_caps(dev);
> +
>          return 0;
>   }
>
> @@ -1361,6 +1389,7 @@ static void do_pci_disable_device(struct pci_dev *dev)
>          }
>
>          pcibios_disable_device(dev);
> +       pci_disable_dev_caps(dev);
>   }
>
>   /**
> --
> 1.6.0.rc1
>
> --
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