Re: [PATCH v11 3/3] DMA: Freescale: update driver to support 8-channelDMA engine

[Hongbo Zhang]

On 11/12/2013 08:09 AM, Dan Williams wrote:
> On Mon, Nov 11, 2013 at 1:12 AM, Hongbo Zhang
> <hongbo.zhang@xxxxxxxxxxxxx> wrote:
> > > > > > diff --git a/drivers/dma/fsldma.c b/drivers/dma/fsldma.c
> > > > > > index 49e8fbd..16a9a48 100644
> > > > > > --- a/drivers/dma/fsldma.c
> > > > > > +++ b/drivers/dma/fsldma.c
> > > > > > @@ -1261,7 +1261,9 @@ static int fsl_dma_chan_probe(struct
> > > > > > fsldma_device
> > > > > > *fdev,
> > > > > >         WARN_ON(fdev->feature != chan->feature);
> > > > > >           chan->dev = fdev->dev;
> > > > > > -    chan->id = ((res.start - 0x100) & 0xfff) >> 7;
> > > > > > +    chan->id = (res.start & 0xfff) < 0x300 ?
> > > > > > +           ((res.start - 0x100) & 0xfff) >> 7 :
> > > > > > +           ((res.start - 0x200) & 0xfff) >> 7;
> > > > > >         if (chan->id >= FSL_DMA_MAX_CHANS_PER_DEVICE) {
> > > Isn't it a bit fragile to have this based on the resource address?
> > > Can't device tree tell you the channel id directly by an index into
> > > the "dma0: dma@100300" node?
> >
> > Yes, both this way and putting a "cell-index" into device tree work.
> > This won't be fragile, because the resource address should always be defined
> > correctly, otherwise even if we can tell a channel id by "cell-index" but
> > with wrong resource address, nothing will work.
> > This piece of code only doesn't seem as neat as using "cell-index", but we
> > prefer the style that let the device tree describes as true as what hardware
> > really has. This doesn't mean "cell-index" isn't acceptable, if it is
> > necessary and unavoidable, we can send another patch to add it, but
> > currently there is no need and we don't have to do this.
> I'm pointing it out because we just had a bug fix to another driver
> motivated by the fact that resource addresses may move from one
> implementation to another, whereas the cell index provided by device
> tree is static.  Just a note, no need to fix it now.

Get it, and will remember it, thank you Dan.
> --
> Dan



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