netdev - Re: [PATCH 1/7] pci: Add PCI LRDT tag size and section size

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Message-Id: <1267126561.2107.13.camel@achroite.uk.solarflarecom.com>
Date:	Thu, 25 Feb 2010 19:36:01 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Matt Carlson <mcarlson@...adcom.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"andy@...yhouse.net" <andy@...yhouse.net>,
	Michael Chan <mchan@...adcom.com>
Subject: Re: [PATCH 1/7] pci: Add PCI LRDT tag size and section size

On Thu, 2010-02-25 at 11:11 -0800, Matt Carlson wrote:
> On Thu, Feb 25, 2010 at 10:53:45AM -0800, Stephen Hemminger wrote:
[...]
> > Shouldn't the function take the pci resource not just the register.
> 
> The functions are designed to operate on a buffer of VPD data, not from
> the hardware directly.
> 
> > And finally, how common is this or is it just something unique to your hw.
> 
> The VPD area is defined by the PCI specs, in the section noted in the
> comment above.  The definitions and functions introduced in this patchset
> should be usable by any driver.  I stopped short of modifying other
> drivers, but I certainly could have.
> 
> However, there are two approaches taken as to how the VPD data is
> extracted and used.  Drivers like tg3 and bnx2 load the VPD data into
> a buffer and operate on that.  Other drivers like niu navigate the VPD
> by loading a dword at a time.  This API would cover the former
> implementation which I've only found to be used by the tg3 and bnx2
> drivers so far.

VPD *access* can be done generically through pci_read_vpd() and
pci_write_vpd(), which use struct pci_vpd_ops.  Currently the only
implementation of pci_vpd_ops is for standard PCI 2.2 VPD.  Other
implementations could be provided for PCI 2.1 VPD or non-standard access
methods.

VPD *parsing* is currently left to user-space (lspci etc.) and to a few
drivers that need it for some reason.

I notice that bnx2 and tg3 are not using pci_read_vpd().  Presumably
this is an optimisation?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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