Re: [PATCH v3 4/6] dma: rcar-dma: use result of updated get_residue in tx_status

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Vinod,

On Monday 12 October 2015 20:42:32 Vinod Koul wrote:
> On Tue, Sep 29, 2015 at 10:44:46PM +0200, hamzahfrq.sub@gmail.com wrote:
> > From: Muhammad Hamza Farooq <mfarooq@visteon.com>
> > 
> > Signed-off-by: Muhammad Hamza Farooq <mfarooq@visteon.com>
> > ---
> > 
> >  drivers/dma/sh/rcar-dmac.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> > index 6c806d0..0b5a367 100644
> > --- a/drivers/dma/sh/rcar-dmac.c
> > +++ b/drivers/dma/sh/rcar-dmac.c
> > @@ -1258,6 +1258,10 @@ static enum dma_status rcar_dmac_tx_status(struct
> > dma_chan *chan,> 
> >  	residue = rcar_dmac_chan_get_residue(rchan, cookie);
> >  	spin_unlock_irqrestore(&rchan->lock, flags);
> > 
> > +	/* if there's no residue, the cookie is complete */
> > +	if (!residue)
> > +		return DMA_COMPLETE;
> > +
> 
> why would we get this, you should not be here if the status is complete and
> exited before you checked the status

The status check is a software check, while the residue check reads hardware 
registers. The hardware might have complete the transfer but the interrupt 
handler might not have had a chance to run yet.

Is it valid from a DMA engine API point of view to return a DMA_IN_PROGRESS 
status with a 0 residue ?

-- 
Regards,

Laurent Pinchart