Re: [PATCH] spi: davinci: Allow device tree devices to use DMA

[David Lechner]

On 11/21/2016 02:37 AM, Sekhar Nori wrote:
> On Sunday 20 November 2016 10:31 PM, David Lechner wrote:
>
> > On 11/20/2016 06:59 AM, Sekhar Nori wrote:
>
> > > On Saturday 19 November 2016 10:11 AM, David Lechner wrote:
>
> > > > @@ -400,6 +401,9 @@ static int davinci_spi_of_setup(struct spi_device
> > > > *spi)
> > > >          if (!of_property_read_u32(np, "ti,spi-wdelay", &prop))
> > > >              spicfg->wdelay = (u8)prop;
> > > >          spi->controller_data = spicfg;
> > > > +        /* Use DMA for device if master supports it */
> > > > +        if (dspi->dma_rx)
> > >
> > > This should be
> > >
> > >         if (!(IS_ERR(dpsi->dma_rx) || IS_ERR(dspi->dma_tx))
> >
> >
> > There is the following code in davinci_spi_probe():
> >
> >     ret = davinci_spi_request_dma(dspi);
> >     if (ret == -EPROBE_DEFER) {
> >         goto free_clk;
> >     } else if (ret) {
> >         dev_info(&pdev->dev, "DMA is not supported (%d)\n", ret);
> >         dspi->dma_rx = NULL;
> >         dspi->dma_tx = NULL;
> >     }
> >
> > So, I does not look like it is possible to get anything other than NULL
> > or a valid pointer for dpsi->dma_rx and that checking dpsi->dma_tx is
> > not necessary.
> >
> > So, I think if (dspi->dma_rx) is sufficient. In fact the same check is
> > used during unwinding if the probe function fails.
>
> You are right, I see it now. Setting dma_rx to NULL overriding the error
> value is confusing since dma_request_chan() itself does not use NULL as
> an error value.
>
> I think it is better to fix the existing code to remove the NULL
> overwrite and use IS_ERR() instead. You should probably wait for some
> feedback from the SPI maintainer though.
>
> Thanks,
> Sekhar


There don't seem to be any further comments. Using NULL here makes more 
sense to me, so I am inclined to leave this patch as-is.