[OASIS Issue Tracker] (VIRTIO-139) pci: missing documentation for dealing with 64 bit config fields

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/VIRTIO-139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=59297#comment-59297 ] 

Rusty Russell commented on VIRTIO-139:
--------------------------------------

We already refer to this in the spec, but not here:

  Drivers MUST NOT assume reads from
  fields greater than 32 bits wide are atomic, nor are reads from
  multiple fields: drivers SHOULD read device configuration space fields like so:

So, I approve of this clarification.

> pci: missing documentation for dealing with 64 bit config fields
> ----------------------------------------------------------------
>
>                 Key: VIRTIO-139
>                 URL: https://issues.oasis-open.org/browse/VIRTIO-139
>             Project: OASIS Virtual I/O Device (VIRTIO) TC
>          Issue Type: Bug
>    Affects Versions: virtio 1.0 cs02
>            Reporter: Michael Tsirkin
>
> pci spec says what width access to use for 32, 16 and 8
> bit fields, but does not explicitly say what to do for
> 32 bit fields. As some implementations might not be able to generate 64 bit accesses,  either allow both 32 and 64 bit
> accesses, or require two 32-bit accesses.



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