Re: SATA resume slowness, e1000 MSI warning

Michael S. Tsirkin
2007-03-12T04:34:44Z

> Quoting Eric W. Biederman <ebiederm@xmission.com>:
> Subject: Re: SATA resume slowness, e1000 MSI warning
>
> "Michael S. Tsirkin" <mst@mellanox.co.il> writes:
>
> > OK I guess. I gather we assume writing read-only registers has no side effects?
> > Are there rumors circulating wrt to these?
>
> I haven't heard anything about that, and if we are writing the same value back
> it should be pretty safe.
>
> I have heard it asserted that at least one version of the pci spec
> only required 32bit accesses to be supported by the hardware. One of
> these days I will have to look that and see if it is true.

Maybe. But surely before the PCI-X days.

> I do know
> it can be weird for hardware developers to support multiple kinds of
> decode.

Is this the only place where Linux uses pci_read_config_word/pci_read_config_dword?
I think such hardware will be pretty much DOA on all OS-es. Why don't we wait
and see whether someone reports a broken config?

> As I recall for pci and pci-x at the hardware level the only
> difference in between 32bit transactions and smaller ones is the state
> of the byte-enable lines.

True, and same holds for PCI-Express.

So let's assume hardware implements RO correctly but ignores the BE bits -
nothing bad happens then, right?

--
MST