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SubjectRE: [PATCH v7 1/2] Documentation: DT: dma: Add Xilinx zynqmp dma device tree binding documentation
Date
Hi Lars,

Thanks for the review...

> -----Original Message-----
> From: Lars-Peter Clausen [mailto:lars@metafoo.de]
> Sent: Wednesday, April 27, 2016 6:10 PM
> To: Appana Durga Kedareswara Rao <appanad@xilinx.com>;
> robh+dt@kernel.org; pawel.moll@arm.com; mark.rutland@arm.com;
> ijc+devicetree@hellion.org.uk; galak@codeaurora.org; Michal Simek
> <michals@xilinx.com>; Soren Brinkmann <sorenb@xilinx.com>;
> vinod.koul@intel.com; dan.j.williams@intel.com; moritz.fischer@ettus.com;
> laurent.pinchart@ideasonboard.com; luis@debethencourt.com; Anirudha
> Sarangi <anirudh@xilinx.com>; Punnaiah Choudary Kalluri
> <punnaia@xilinx.com>
> Cc: devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> kernel@vger.kernel.org; dmaengine@vger.kernel.org
> Subject: Re: [PATCH v7 1/2] Documentation: DT: dma: Add Xilinx zynqmp dma
> device tree binding documentation
>
> On 04/27/2016 09:33 AM, Appana Durga Kedareswara Rao wrote:
> > Hi Lars,
> >
> >> -----Original Message-----
> >> From: Lars-Peter Clausen [mailto:lars@metafoo.de]
> >> Sent: Wednesday, April 27, 2016 12:42 PM
> >> To: Appana Durga Kedareswara Rao <appanad@xilinx.com>;
> >> robh+dt@kernel.org; pawel.moll@arm.com; mark.rutland@arm.com;
> >> ijc+devicetree@hellion.org.uk; galak@codeaurora.org; Michal Simek
> >> <michals@xilinx.com>; Soren Brinkmann <sorenb@xilinx.com>;
> >> vinod.koul@intel.com; dan.j.williams@intel.com; Appana Durga
> >> Kedareswara Rao <appanad@xilinx.com>; moritz.fischer@ettus.com;
> >> laurent.pinchart@ideasonboard.com; luis@debethencourt.com; Anirudha
> >> Sarangi <anirudh@xilinx.com>; Punnaiah Choudary Kalluri
> >> <punnaia@xilinx.com>
> >> Cc: devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> >> linux- kernel@vger.kernel.org; dmaengine@vger.kernel.org
> >> Subject: Re: [PATCH v7 1/2] Documentation: DT: dma: Add Xilinx zynqmp
> >> dma device tree binding documentation
> >>
> >> On 04/27/2016 09:05 AM, Kedareswara rao Appana wrote:
> >> [...]
> >>> +- 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,src-burst-len : AXI length for data read. Support only power of
> >>> + 2 byte values.
> >>> +- xlnx,dst-burst-len : AXI length for data write. Support only power of
> >>
> >> These are all software runtime configuration parameters that you'd
> >> want to change at runtime depending on which peripheral you are
> >> targeting with a specific DMA transfer. These really do not belong into the
> devicetree.
> >
> > You mean to have a separate config structure in the driver and handle
> > the above parameters Through that structure???
> >
> > I understand that above will work for slave dma transfer types what
> > about memory to memory Transfers where we don't have provision to the use
> this parameters...
>
> These parameters are just as application specific as e.g. the DMA
> source/destination address or the DMA transfer length. If you want to use the
> DMA controller in a different configuration you'd have to re-compile the DTB
> and reboot your board, that is not really practical. Especially considering that
> you'd typically have multiple applications using the DMA controller in different
> configurations concurrently. In general if I have to reconfigure the DT depending
> on what application software is running something is fundamentally broken.
>
> Derive these parameters at runtime depending on the requested transfer. E.g.
> some transfer types only work in SG mode, others only work in non-SG modes.
> For those which can work in both modes choose the one that is more efficient.
> Similar for the other parameters.

Ok will fix in the next version...
Will use module_params for the above properties.

Regards,
Kedar.

>
> - Lars

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