Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 16 Oct 2020 12:36:18 +0530
From:   Vinod Koul <vkoul@kernel.org>
To:     Eugen.Hristev@microchip.com
Cc:     robh@kernel.org, Tudor.Ambarus@microchip.com,
        Ludovic.Desroches@microchip.com, dmaengine@vger.kernel.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, Nicolas.Ferre@microchip.com
Subject: Re: [PATCH 6/7] dt-bindings: dmaengine: at_xdmac: add optional
 microchip,m2m property
Message-ID: <20201016070618.GW2968@vkoul-mobl>
References: <20200914140956.221432-1-eugen.hristev@microchip.com>
 <20200914140956.221432-7-eugen.hristev@microchip.com>
 <20200922233327.GA3474555@bogus>
 <6f305564-e91c-794b-0025-de805f1d1a58@microchip.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <6f305564-e91c-794b-0025-de805f1d1a58@microchip.com>
Precedence: bulk

Hi Eugen,

On 16-10-20, 06:45, Eugen.Hristev@microchip.com wrote:
> On 23.09.2020 02:33, Rob Herring wrote:
> 
> > On Mon, Sep 14, 2020 at 05:09:55PM +0300, Eugen Hristev wrote:
> >> Add optional microchip,m2m property that specifies if a controller is
> >> dedicated to memory to memory operations only.
> >>
> >> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
> >> ---
> >>   Documentation/devicetree/bindings/dma/atmel-xdma.txt | 6 ++++++
> >>   1 file changed, 6 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/dma/atmel-xdma.txt b/Documentation/devicetree/bindings/dma/atmel-xdma.txt
> >> index 510b7f25ba24..642da6b95a29 100644
> >> --- a/Documentation/devicetree/bindings/dma/atmel-xdma.txt
> >> +++ b/Documentation/devicetree/bindings/dma/atmel-xdma.txt
> >> @@ -15,6 +15,12 @@ the dmas property of client devices.
> >>       interface identifier,
> >>       - bit 30-24: PERID, peripheral identifier.
> >>
> >> +Optional properties:
> >> +- microchip,m2m: this controller is connected on AXI only to memory and it's
> >> +     dedicated to memory to memory DMA operations. If this option is
> >> +     missing, it's assumed that the DMA controller is connected to
> >> +     peripherals, thus it's a per2mem and mem2per.
> > 
> > Wouldn't 'dma-requests = <0>' cover this case?
> > 
> > Rob
> > 
> 
> Hi Rob,
> 
> I do not think so. With requests = 0, it means that actually the DMA 
> controller is unusable ?
> Since you suggest requests = 0, it means that it cannot take requests at 
> all ?
> I do not find another example in current DT with this property set to zero.

Not really, dma-requests implies "request signals supported" which are
used for peripheral cases. m2m does not need request signals, so it is
very reasonable to conclude that dma-requests = <0> would imply no
peripheral support and only m2m support.

Thanks
-- 
~Vinod