Subject: Re: Debian ports for RiscPC, ARM710, etc.

From: Russell King <[email-masked]>
Date: Thu, 1 Oct 1998 08:51:13 +0100 (BST)

Philip Blundell said:
> >BTW, DMA doesn't seem to work with this drive (Conner CFS1081A) - does anyone
> 
> What happens when you try to turn it on?  Some drives do seem to claim to be 
> able to do DMA but actually fail every transfer if you use it.

It doesn't work. (it times out with an IRQ status of 0).

> > BuffType=0(?), BuffSize=0KB, MaxMultSect=16, MultSect=off
> > DblWordIO=no, maxPIO=1(medium), DMA=yes, maxDMA=2(fast)
> 
> It looks like the drive certainly thinks it supports DMA.  But the IDE driver 
> almost certainly doesn't know about the cache coherency issues involved.

Hmm.  However, the IDE driver does not use the normal enable_dma() functions.

--
Russell King ([email-masked])

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From: Philip Blundell <[email-masked]>
Date: Thu, 01 Oct 1998 10:37:59 +0100

>Hmm.  However, the IDE driver does not use the normal enable_dma() functions.

No, it wouldn't.  The enable/disable_dma functions are only for slave DMA.  
Busmaster devices (ie most PCI ones) do everything themselves.  So the IDE 
driver needs to do the cache coherency by hand, same as PCI ethernet and SCSI 
drivers do.

p.