Re: SunFire v100 / Acer M5229 IDE DMA error workaround

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Oct 30, 2008 at 03:42:00PM -0400, Rafal Boni wrote:
> > As you guessed, this won't work for ATAPI. For ATAPI devices, we may have
> > short xfers, where we interrupt with the DMA channels still active.
> 
> Let me ask a couple potentially stupid questions:
> 
>       1. How does one differentiate between a succesfull (completed)
>          transfer and short xfer?  In other words, is there a status
>          bit that indicates short xfer?

A for a successull xfer the DMA active bit will be cleared at interrupt time.
For a short xfer it will not.

>          Should IDEDMA_CTL_ERR be
>          set in that case?

Not, it's not an error in the sense that all transfered bits have been
successfully transfered from/to device. It just means the device
sent/requested less bytes than what was programmed in the DMA engine.

> 
>       2. Presumably we know if this is an ATA or ATAPI DMA request;
>          would this be any less bothersome to you if we only did
>          this for pure ATA requests? (and obviously made it chip-
>          specific).

Yes. 

> 
>       3. Can you give me a good way to try and provoke short xfers
>          with ATAPI? 

I think it happens on regular usage of a CD drive (mounting it
for example).

> I suspect that on this controller / machine
>          that ATAPI DMA is in general broken, see below:
> 
>     aceride0:0:0: lost interrupt
>           type: atapi tc_bcount: 32 tc_skip: 0
>     aceride0:0:0: bus-master DMA error: missing interrupt, status=0x21
>     cd0: transfer error, downgrading to Ultra-DMA mode 1
>     cd0(aceride0:0:0): using PIO mode 4, Ultra-DMA mode 1 (using DMA)
>     aceride0:0:0: lost interrupt
>           type: atapi tc_bcount: 32 tc_skip: 0
>     aceride0:0:0: bus-master DMA error: missing interrupt, status=0x21
>     cd0: transfer error, downgrading to PIO mode 4
>     cd0(aceride0:0:0): using PIO mode 4

Quite possible; not all controllers support DMA for non-ATA commands, and
I don't have a definitive list ...

> > > + bus_space_write_1(sc->sc_dma_iot, cp->dma_iohs[IDEDMA_CTL], 0, status);
> > > +
> > >   if ((status & IDEDMA_CTL_ERR) != 0 && force != WDC_DMAEND_ABRT_QUIET) {
> > >           aprint_error("%s:%d:%d: bus-master DMA error: status=0x%x\n",
> > >               device_xname(sc->sc_wdcdev.sc_atac.atac_dev), channel,
> > 
> > this is done by pciide_irqack(). It should not be done there.
> 
> Yeah, I removed this; it didn't help without the above change and with the
> above change present, the absence/presence of this change didn't make any
> difference.

good.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--