Re: [PATCH v2 2/6] dt-bindings: dma: dw: Add max burst transaction length property

Serge Semin
2020-05-15T11:11:20Z

On Fri, May 15, 2020 at 04:26:58PM +0530, Vinod Koul wrote:
> On 15-05-20, 13:51, Andy Shevchenko wrote:
> > On Fri, May 15, 2020 at 11:39:11AM +0530, Vinod Koul wrote:
> > > On 12-05-20, 15:38, Andy Shevchenko wrote:
> > > > On Tue, May 12, 2020 at 02:49:46PM +0300, Serge Semin wrote:
> > > > > On Tue, May 12, 2020 at 12:08:04PM +0300, Andy Shevchenko wrote:
> > > > > > On Tue, May 12, 2020 at 12:35:31AM +0300, Serge Semin wrote:
> > > > > > > On Tue, May 12, 2020 at 12:01:38AM +0300, Andy Shevchenko wrote:
> > > > > > > > On Mon, May 11, 2020 at 11:05:28PM +0300, Serge Semin wrote:
> > > > > > > > > On Fri, May 08, 2020 at 02:12:42PM +0300, Andy Shevchenko wrote:
> > > > > > > > > > On Fri, May 08, 2020 at 01:53:00PM +0300, Serge Semin wrote:
> >
> > ...
> >
> > > > I leave it to Rob and Vinod.
> > > > It won't break our case, so, feel free with your approach.
> > >
> > > I agree the DT is about describing the hardware and looks like value of
> > > 1 is not allowed. If allowed it should be added..
> >
> > It's allowed at *run time*, it's illegal in *pre-silicon stage* when
> > synthesizing the IP.
>
> Then it should be added ..

Vinod, max-burst-len is "MAXimum" burst length not "run-time or current or any
other" burst length. It's a constant defined at the IP-core synthesis stage and
according to the Data Book, MAX burst length can't be 1. The allowed values are
exactly as I described in the binding [4, 8, 16, 32, ...]. MAX burst length
defines the upper limit of the run-time burst length. So setting it to 1 isn't
about describing a hardware, but using DT for the software convenience.

-Sergey

>
> --
> ~Vinod