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

Andy Shevchenko
2020-05-11T21:02:08Z

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:
> > > This array property is used to indicate the maximum burst transaction
> > > length supported by each DMA channel.
> >
> > > + snps,max-burst-len:
> > > + $ref: /schemas/types.yaml#/definitions/uint32-array
> > > + description: |
> > > + Maximum length of burst transactions supported by hardware.
> > > + It's an array property with one cell per channel in units of
> > > + CTLx register SRC_TR_WIDTH/DST_TR_WIDTH (data-width) field.
> > > + items:
> > > + maxItems: 8
> > > + items:
> >
> > > + enum: [4, 8, 16, 32, 64, 128, 256]
> >
> > Isn't 1 allowed?
>
> Burst length of 1 unit is supported, but in accordance with Data Book the MAX
> burst length is limited to be equal to a value from the set I submitted. So the
> max value can be either 4, or 8, or 16 and so on.

Hmm... It seems you mistakenly took here DMAH_CHx_MAX_MULT_SIZE pre-silicon
configuration parameter instead of runtime as described in Table 26:
CTLx.SRC_MSIZE and DEST_MSIZE Decoding.

--
With Best Regards,
Andy Shevchenko