Re: [Xen-devel] [PATCH][RFC] Support more Capability Structures andDevice Specific

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Yuji Shimada writes ("Re: [Xen-devel] [PATCH][RFC] Support more Capability 
Structures andDevice Specific"):
> In my patch, registers inside Vendor Specific Capability Structure
> (Capability ID is 09h) are all passthrough, except Next Capability
> Pointer Register.

My worry is that a device may say, in its vendor-specific
register-level programming documentation for these configurations,
something like:

  Do _not_ set USE_EXTERNAL_INPUT and USE_INTERNAL_INPUT
  simultaneously; this may cause damage to the Gnomovision PCI
  card and may also cause the Gnomovision PCI card to draw
  excessive current from the host power supply.

Or

  Do _not_ use the UPLOAD_FIRMWARE_* configuration.  These are for use
  by the approved Gnomovision firmware loader only.  Uploading bad
  firmware may cause damage [etc. etc.]

I haven't read many modern PCI card specs but with the constant
shifting of functionality (even functionality which is intended to
preserve hardware integrity) to software and firmware, I would be wary
of assuming that every unknown PCI card has no register and
configuration settings which can cause hardware damage or other kinds
of unexpected and undesirable events.

If there is there a requirement written into the general PCI
specification that this won't happen, then fine - if so please quote
chapter and verse.

Ian.

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