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SubjectRe: [PATCH] pci: Update VPD size with correct length
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On 10/23/2015 02:09 AM, Hannes Reinecke wrote:
> PCI-2.2 VPD entries have a maximum size of 32k, but might actually
> be smaller than that. To figure out the actual size one has to read
> the VPD area until the 'end marker' is reached.
> Trying to read VPD data beyond that marker results in 'interesting'
> effects, from simple read errors to crashing the card.
> This path modifies the attribute size to the avialable VPD size.
>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---
> drivers/pci/access.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 6bc9b12..4f8208e 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -409,6 +409,34 @@ static int pci_vpd_f0_dev_check(struct pci_dev *dev)
> return ret;
> }
>
> +/**
> + * pci_vpd_size - determine actual size of Vital Product Data
> + * @dev: pci device struct
> + * @old_size: current assumed size, also maximum allowed size
> + *
> + */
> +size_t
> +pci_vpd_pci22_size(struct pci_dev *dev, size_t old_size)
> +{
> + loff_t off = 0;
> + unsigned char header[1+2]; /* 1 byte tag, 2 bytes length */
> +
> + while (off < old_size && pci_read_vpd(dev, off, 1, header)) {
> + if (header[0] == 0x78) /* End tag descriptor */
> + return off + 1;
> + if (header[0] & 0x80) {
> + /* Large Resource Data Type Tag */
> + if (pci_read_vpd(dev, off+1, 2, &header[1]) != 2)
> + return off + 1;
> + off += 3 + ((header[2] << 8) | header[1]);
> + } else {
> + /* Short Resource Data Type Tag */
> + off += 1 + (header[0] & 0x07);
> + }
> + }
> + return old_size;
> +}
> +

My understanding is that the end tag can have some data associated with
it such as a checksum. What you may want to look at doing is process
long tag and short tag bits first. Then you could do a mask and compare
after and if ((header[0] & ~0x7) == 0x78) then you return off + 1.

Also I was wondering if you have looked at the cxgb4 network driver?
They are using the vpd read/write calls to access their EEPROM and I
assume they are doing so outside the actual VPD fields.

- Alex


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