linux-kernel - Re: [PATCH] libata: Add MMIO support to pata

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Date:	Fri, 15 Feb 2008 22:27:25 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	benh@...nel.crashing.org
Cc:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Tim Ellis <tim@...dg.com>, linux-kernel@...r.kernel.org,
	jeff@...zik.org
Subject: Re: [PATCH] libata: Add MMIO support to pata_sil680

> The dbdma start is mostly harmless (things don't get posted for -that-
> long), though I suppose it's worth fixing. Would reading back dmactl do
> in that case or do you foresee any kind of side effect ? (Maybe only
> doing it for MMIO ?)

The dmactl read back should be just fine, or any other DMA register (eg
status).

> As for SRST, I'm not totally confident how safe it is to read back
> there while doing the reset sequence, so I'm tempted to really only
> do it for MMIO and use altstat rather than ctl/stat (the later tends
> to have side effects which we don't want here).

Agreed - we know some controllers crap themselves spectacularly on
anything which causes a SATA data transfer to be needed during a reset so
the status is probably safest. The fact its not fixed is because nobody
has sat down to figure out what is safe.

> The main problem from here is that I don't know whether we are using
> MMIO or PIO from libata-core. Maybe I can add a host flag indicate
> that such flushing is needed ?

Easier to add that to the ioxxxx ops I suspect (ioispio/ioismmio say) ?

Alan
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