netdev - Re: [Intel-wired-lan] [PATCH] pci: Limit VPD reads for all Intel Ethernet devices

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Message-ID: <555B5CBF.1090902@redhat.com>
Date:	Tue, 19 May 2015 08:54:39 -0700
From:	Alexander Duyck <alexander.h.duyck@...hat.com>
To:	Mark D Rustad <mark.d.rustad@...el.com>, bhelgaas@...gle.com
CC:	linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
	netdev@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH] pci: Limit VPD reads for all Intel
 Ethernet devices

On 05/18/2015 05:00 PM, Mark D Rustad wrote:
> To save boot time and some memory, limit VPD size to the maximum
> possible for all Intel Ethernet devices that have VPD, which is 1K.
>
> Signed-off-by: Mark Rustad <mark.d.rustad@...el.com>
> Acked-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>   drivers/pci/quirks.c |    7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index c6dc1dfd25d5..4fabbeda964a 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -1903,12 +1903,15 @@ static void quirk_netmos(struct pci_dev *dev)
>   DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_NETMOS, PCI_ANY_ID,
>   			 PCI_CLASS_COMMUNICATION_SERIAL, 8, quirk_netmos);
>   
> -static void quirk_e100_interrupt(struct pci_dev *dev)
> +static void quirk_intel_enet(struct pci_dev *dev)
>   {
>   	u16 command, pmcsr;
>   	u8 __iomem *csr;
>   	u8 cmd_hi;
>   
> +	if (dev->vpd)
> +		dev->vpd->len = 0x400;
> +
>   	switch (dev->device) {
>   	/* PCI IDs taken from drivers/net/e100.c */
>   	case 0x1029:
> @@ -1967,7 +1970,7 @@ static void quirk_e100_interrupt(struct pci_dev *dev)
>   	iounmap(csr);
>   }
>   DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
> -			PCI_CLASS_NETWORK_ETHERNET, 8, quirk_e100_interrupt);
> +			      PCI_CLASS_NETWORK_ETHERNET, 8, quirk_intel_enet);
>   
>   /*
>    * The 82575 and 82598 may experience data corruption issues when transitioning
>

I wasn't a fan of the first VPD patch and this clinches it.  What I 
would recommend doing is identifying all of the functions for a given 
device that share a VPD and then eliminate the VPD structure for all but 
the first function.  By doing that the OS should treat the other 
functions as though their VPD areas don't exist.

The way I would code it would be to scan for any other functions with 
the same bus and device number and if one with a lower function number 
has a VPD area we delete our own VPD area, if one with a higher function 
number has a VPD area then we delete that ones VPD area, if the search 
returns our function number we resume our search from there, and do 
nothing if no other devices with VPD are found. The general idea is to 
sort things until the device closest to function 0 is the only one with 
a VPD area.

Artificially limiting the size of the VPD does nothing but cut off 
possibly useful data, you would be better of providing all of the data 
on only the first function than providing only partial data on all 
functions and adding extra lock overhead.

- Alex
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