linux-kernel - Re: [PATCH v4 1/2] Documentation: dt: Add Xilinx zynqmp dma device tree binding documentation

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Message-ID: <CAGnW=Bb-vwvwAm7ztH1XLqRHbVx+5MWZJd=fDgOoqJ7Qtyo=nw@mail.gmail.com>
Date:	Tue, 25 Aug 2015 00:09:16 +0530
From:	punnaiah choudary kalluri <punnaia@...inx.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Punnaiah Choudary Kalluri <punnaiah.choudary.kalluri@...inx.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"michal.simek@...inx.com" <michal.simek@...inx.com>,
	Vinod Koul <vinod.koul@...el.com>, dan.j.williams@...el.com,
	dmaengine@...r.kernel.org,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punnaiah Choudary <kpc528@...il.com>
Subject: Re: [PATCH v4 1/2] Documentation: dt: Add Xilinx zynqmp dma device
 tree binding documentation

On Mon, Aug 24, 2015 at 7:17 PM, Lars-Peter Clausen <lars@...afoo.de> wrote:
> On 08/06/2015 05:19 AM, Punnaiah Choudary Kalluri wrote:
> [...]
>> +Optional properties:
>> +- xlnx,include-sg: Indicates the controller to operate in simple or scatter
>> +                gather dma mode
>> +- xlnx,ratectrl: Scheduling interval in terms of clock cycles for
>> +              source AXI transaction
>> +- xlnx,overfetch: Tells whether the channel is allowed to over fetch the data
>> +- xlnx,src-issue: Number of AXI outstanding transactions on source side
>> +- xlnx,desc-axi-cohrnt: Tells whether the AXI transactions generated for the
>> +                     descriptor read are marked Non-coherent
>> +- xlnx,src-axi-cohrnt: Tells whether the AXI transactions generated for the
>> +                     source descriptor payload are marked Non-coherent
>> +- xlnx,dst-axi-cohrnt: Tells whether the AXI transactions generated for the
>> +                     dst descriptor payload are marked Non-coherent
>> +- xlnx,desc-axi-qos: AXI QOS bits to be used for descriptor fetch
>> +- xlnx,src-axi-qos: AXI QOS bits to be used for data read
>> +- xlnx,dst-axi-qos: AXI QOS bits to be used for data write
>> +- xlnx,desc-axi-cache: AXI cache bits to be used for descriptor fetch.
>> +- xlnx,desc-axi-cache: AXI cache bits to be used for data read
>> +- xlnx,desc-axi-cache: AXI cache bits to be used for data write
>> +- xlnx,src-burst-len: AXI length for data read. Support only power of 2 values
>> +                   i.e 1,2,4,8 and 16
>> +- xlnx,dst-burst-len: AXI length for data write. Support only power of 2 values
>> +                   i.e 1,2,4,8 and 16
>
> None of these really belong into the devicetree. This is all runtime
> configuration data.

This is a general purpose dma and provides more flexibility to the
user for configuring the
descriptor, data and bus parameters. one way is as you said these
parameters can be
configured at runtime but i didn't find a way configuring the channel
at runtime for mem to
mem transfers. I have checked the  device_config function description
and it is strictly
meant for slave operations only. So, i didn't see anything wrong
having these parameter values
from the device tree as these all are hw parameters.

Regards,
Punnaiah

>
> - Lars
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