Re: [PATCH] parport_pc.c PnP BIOS sanity check

[Thomas Hood <jdthoodREMOVETHIS@yahoo.co.uk>]

Thanks for the replies.

I'd like to underline Alan Cox's reply that DMA0 _is_ usable.
In fact, my sound chip is configured to use DMA0.

If (and only if) parport _cannot_ use DMA0 for some reason
then the sanity check is justified.  In that case I'd just ask
that a short comment be added to the code that gives the reason.

Cheers
Thomas

Ignacio Vazquez-Abrams wrote:
> DMA0 is reserved for memory refresh. It _can't_ be used for anything else,
> therefore a value of 0 is representative of no value whatsoever.

Alan Cox wrote:
> This has been unsafe since about 1995, when DMA 0 became available as PC's
> stopped using the ISA DMA engine for memory refresh (a very neat original PC
> hack)

Gunther Mayer wrote:
> 1)
>   I think I saw some BIOS report DMA0 for "none" (could even have
>   been ACPI which is returning PNP formatted legacy resource data).
> 2)
>   I have never seen DMA0 for parport configured by a BIOS.
> 3)
>   Try "lssuperio" if you want the real hardware thing.
> 
> This qualifies the code as it is as a sanity check.