Re: [PATCH 2/2] dw_dmac: add cyclic API to DW DMA driver

[Haavard Skinnemoen <haavard.skinnemoen@atmel.com>]

Sosnowski, Maciej wrote:
> > +void dw_dma_cyclic_stop(struct dma_chan *chan)
> > +{
> > +	struct dw_dma_chan	*dwc = to_dw_dma_chan(chan);
> > +	struct dw_dma		*dw = to_dw_dma(dwc->chan.device);
> > +
> > +	channel_clear_bit(dw, CH_EN, dwc->mask);
> > +	while (dma_readl(dw, CH_EN) & dwc->mask)
> > +		cpu_relax();
> > +}  
> 
> Don't you need locks in dw_dma_cyclic_stop?

Good question. On one hand, if cyclic_start() can race with
cyclic_stop(), the client probably has more serious issues to deal
with. On the other hand, if something ever manages to set the CH_EN bit
at the wrong moment, the loop may never finish.

So it's probably safest to wrap it in spin_lock_bh(). You should
probably add a note that this function can not be called from interrupt
context too.

Haavard