Re: [RFC PATCH] nForce4 ADMA with NCQ: It's aliiiive..

[Jens Axboe <jens.axboe@oracle.com>]

On Tue, Oct 10 2006, Robert Hancock wrote:
> Allen Martin wrote:
> >>But I really don't think that is necessary.  I will take a 
> >>look at docs and see how things match up, when I am much more 
> >>awake.  Most likely you need to be using another set of 
> >>registers, and be all MMIO, all the time.
> >
> >You shouldn't be touching BM registers when ADMA is enabled, it can
> >cause bad things to happen.
> >
> >You should be using BM registers when doing ATAPI protocol though, as it
> >doesn't work through ADMA.  So I wouldn't say you should be using MMIO
> >all the time.
> >
> >-Allen
> 
> OK, I've updated the code to take this into account, an updated patch is 
> attached. However, this does raise an issue. If we have to fall back to 
> legacy mode to do ATAPI DMA, this means that we can't do 64-bit DMA for 
> such transfers. Since by the time the driver gets a request the SGs have 
> already been created based on the set DMA mask, the only way I can see 
> to handle this is to either allow ATAPI DMA or 64-bit DMA, not both. 
> I've chosen to default to 64-bit DMA in this version, but there is a 
> module parameter which allows overriding this if you care more about 
> using ATAPI devices than efficiency with over 4GB of RAM. I'm open to 
> suggestions on a better way to handle this..

Should be easily fixable - in general, set 64-bit dma mask. Then when
you detect an atapi device, lower the dma mask settings to 32-bit dma
for that device only. So the pci device in question gets a full 64-bit
dma mask, the attached scsi devices can have lower masks if necessary.
I'd suggest doing this off slave config.

-- 
Jens Axboe