Re: SATA resume slowness, e1000 MSI warning

[Michael S. Tsirkin]

> Quoting Eric W. Biederman <ebiederm@xxxxxxxxxxxx>:
> Subject: Re: SATA resume slowness, e1000 MSI warning
> 
> "Michael S. Tsirkin" <mst@xxxxxxxxxxxxxx> 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
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