Re: [PATCH 1/3] dmaengine: dw-edma: Implement device_synchronize() callback

On Mon, Jun 29, 2026 at 09:20:56AM -0500, Frank Li wrote:
> On Mon, Jun 29, 2026 at 10:45:15AM +0200, Manivannan Sadhasivam via B4 Relay wrote:
> >
> > From: Manivannan Sadhasivam <[email protected]>
> >
> > device_synchronize() callback is required by the client drivers to ensure
> > all the DMA operations are completed so that they can free the memory
> > associated with the complete callbacks.
> >
> > So implement this callback by first making sure that all the in-flight DMA
> > operations are completed and then call vchan_synchronize() to drain the
> > DMA tasklet.
> >
> > Signed-off-by: Manivannan Sadhasivam <[email protected]>
> > ---
> >  drivers/dma/dw-edma/dw-edma-core.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> > index c2feb3adc79f..7b12dfe8cfd3 100644
> > --- a/drivers/dma/dw-edma/dw-edma-core.c
> > +++ b/drivers/dma/dw-edma/dw-edma-core.c
> > @@ -331,6 +331,21 @@ static int dw_edma_device_terminate_all(struct dma_chan *dchan)
> >         return err;
> >  }
> >
> > +static void dw_edma_device_synchronize(struct dma_chan *dchan)
> > +{
> > +       struct dw_edma_chan *chan = dchan2dw_edma_chan(dchan);
> > +       unsigned long timeout = jiffies + msecs_to_jiffies(5000);
> > +
> > +       /*
> > +        * Make sure all the in-flight DMA operations are completed before
> > +        * draining the tasklet using vchan_synchronize().
> > +        */
> > +       while (chan->status == EDMA_ST_BUSY && time_before(jiffies, timeout))
> > +               cpu_relax();
> 
> read_poll_timeout(...),  Does need READ_ONCE(chan->status)?
> 

Yeah, makes sense. I'll use:

read_poll_timeout(READ_ONCE, chan->status, chan->status != EDMA_ST_BUSY,
		10, 0, false, chan->status);

- Mani

-- 
மணிவண்ணன் சதாசிவம்