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

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Date:   Fri, 15 May 2020 14:11:12 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Vinod Koul <vkoul@...nel.org>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Williams <dan.j.williams@...el.com>,
        <linux-mips@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] dt-bindings: dma: dw: Add max burst transaction
 length property

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