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


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