Re: [Qemu-devel] [PATCH] ide: fix DMA register transitions

[Kevin Wolf <kwolf@redhat.com>]

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Am 03.08.2016 um 07:06 hat Stefan Weil geschrieben:
> Am 03.08.2016 um 00:05 schrieb John Snow:
> > ATA8-APT defines the state transitions for both a host controller and
> > for the hardware device during the lifecycle of a DMA transfer, in
> > section 9.7 "DMA command protocol."
> > 
> > One of the interesting tidbits here is that when a device transitions
> > from DDMA0 ("Prepare state") to DDMA1 ("Data_Transfer State"), it can
> > choose to set either BSY or DRQ to signal this transition, but not both.
> > 
> > as ide_sector_dma_start is the last point in our preparation process
> > before we begin the real data transfer process (for either AHCI or BMDMA),
> > this is the correct transition point for DDMA0 to DDMA1.
> > 
> > I have chosen !BSY && DRQ for QEMU to make the transition from DDMA0 the
> > most obvious.
> > 
> > Reported-by: Benjamin David Lunt <fys@fysnet.net>
> > Signed-off-by: John Snow <jsnow@redhat.com>
> > ---
> >  hw/ide/core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/hw/ide/core.c b/hw/ide/core.c
> > index d117b7c..e961d42 100644
> > --- a/hw/ide/core.c
> > +++ b/hw/ide/core.c
> > @@ -907,7 +907,7 @@ eot:
> >  
> >  static void ide_sector_start_dma(IDEState *s, enum ide_dma_cmd dma_cmd)
> >  {
> > -    s->status = READY_STAT | SEEK_STAT | DRQ_STAT | BUSY_STAT;
> > +    s->status = READY_STAT | SEEK_STAT | DRQ_STAT;
> >      s->io_buffer_size = 0;
> >      s->dma_cmd = dma_cmd;
> 
> 
> This patch fixes the reported test case, thank you.
> 
> Tested-by: Stefan Weil <sw@weilnetz.de>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Benjamin, you'll still want to fix your driver code. If John had chosen
BSY && !DRQ, which is an equally valid option, qemu would be working
correctly, but your test case would still hang.

Kevin

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