Re: [alsa-devel] [PATCH v5 06/10] dmaengine: add API for getting dma controller's quirk

[Shawn Lin]

å 2015/10/8 16:31, Lars-Peter Clausen åé:
> On 10/06/2015 11:21 AM, Shawn Lin wrote:
> > Hi Vinod,
> >
> > On 2015/10/5 23:37, Vinod Koul wrote:
> > > On Mon, Sep 14, 2015 at 07:48:59AM +0800, Shawn Lin wrote:
> > > > Add dmaengine_get_quirks API for peripheral devices to query
> > > > quirks if they need it to make special workaround due to broken
> > > > dma controller design.
> > > >
> > > > Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> > > > ---
> > > >
> > > > Changes in v5: None
> > > > Changes in v4: None
> > > > Changes in v3: None
> > > > Changes in v2: None
> > > > Changes in v1: None
> > > >
> > > >    include/linux/dmaengine.h | 9 +++++++++
> > > >    1 file changed, 9 insertions(+)
> > > >
> > > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > > > index e2f5eb4..5174ca4 100644
> > > > --- a/include/linux/dmaengine.h
> > > > +++ b/include/linux/dmaengine.h
> > > > @@ -704,6 +704,7 @@ struct dma_device {
> > > >
> > > >        int (*device_config)(struct dma_chan *chan,
> > > >                     struct dma_slave_config *config);
> > > > +    int (*device_get_quirks)(struct dma_chan *chan);
> > >
> > > And why do we want to expose this to users? THis doesnt seem right!
> >
> > Basically I agree not to expose dma's quirk to slave controllers...But, the
> > fact I mentioned on cover letter explain the reasons why I have to let slave
> > controllers know that they are working with a broken dma. It's a dilemma
> > that if we don't want that to be exposed(let slave controllers' driver get
> > the info via a API), we have t add broken quirk for all of them ,here and
> > there, which seems to be a disaster:(
>
> The problem with this API is that it transports values with device specific
> meanings over a generic API. Which is generally speaking not a good idea
> because the consumer witch is supposed to be generic suddenly needs to know
> which provider it is talking to.
>
> A better solution in this case typically is either introduce a generic API
> with generic values or a custom API with custom values, but don't mix the two.
>
> > I would appreciate it if you could give me some suggestions at your earliest
> > convenience. :)
>
> In this case I think the best way to handle this is not quirks, but rather
> expose the actual maximum burst size using the DMA capabilities API. Since
> supporting only a certain burst depth is not really a quirk. All hardware
> has a limit for this and for some it might be larger or smaller than for
> others and it might be the same IP core but the maximum size depends on some
> IP core parameters. So this should be discoverable.

Hi Lars,

Thanks for looking for that.

It's a good idea if all clients of the Soc are broken, but unfortunately 
some of them work. So... max burst shoule be different for individuals.

> - Lars


--
Best Regards
Shawn Lin

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