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SubjectRE: [PATCH v4] dma: Add Xilinx AXI Direct Memory Access Engine driver support
Date
Hi Vinod,


> -----Original Message-----
> From: Appana Durga Kedareswara Rao
> Sent: Monday, January 19, 2015 7:39 PM
> To: 'Arnd Bergmann'; vinod.koul@intel.com
> Cc: linux-arm-kernel@lists.infradead.org; devicetree@vger.kernel.org;
> vinod.koul@intel.com; Srikanth Vemula; linux-kernel@vger.kernel.org;
> Srikanth Thokala; dmaengine@vger.kernel.org; robh+dt@kernel.org; Michal
> Simek; Anirudha Sarangi; grant.likely@linaro.org; dan.j.williams@intel.com
> Subject: RE: [PATCH v4] dma: Add Xilinx AXI Direct Memory Access Engine
> driver support
>
> Hi Arnd,
>
> > -----Original Message-----
> > From: Arnd Bergmann [mailto:arnd@arndb.de]
> > Sent: Friday, October 24, 2014 7:29 PM
> > To: Appana Durga Kedareswara Rao
> > Cc: linux-arm-kernel@lists.infradead.org; devicetree@vger.kernel.org;
> > vinod.koul@intel.com; Srikanth Vemula; linux-kernel@vger.kernel.org;
> > Srikanth Thokala; dmaengine@vger.kernel.org; robh+dt@kernel.org;
> > Michal Simek; Anirudha Sarangi; grant.likely@linaro.org;
> > dan.j.williams@intel.com
> > Subject: Re: [PATCH v4] dma: Add Xilinx AXI Direct Memory Access
> > Engine driver support
> >
> > On Friday 24 October 2014 12:08:26 Appana Durga Kedareswara Rao wrote:
> > > From: Arnd Bergmann [mailto:arnd@arndb.de]
> > > > On Tuesday 21 October 2014 09:06:13 Appana Durga Kedareswara Rao
> > wrote:
> > > > > The above mentioned API's and structures will be used by the
> > > > > dma test client driver's to set hardware configuration information.
> > > > > The dma client drivers are not mainlined yet and it is
> > > > > Internally used by our git-tree to test the DMA functionality in
> loopback .
> > > >
> > > > I would suggest you add the test driver into the main dmaengine
> > > > driver file directly then, so you don't need to export the symbols.
> > > > If there are important reasons to keep that as separate files,
> > > > just move the header to the drivers/dma/ directory and add the
> > > > test driver
> > there.
> > >
> > > Sorry I forgot to mention the below things in the mail .The Config
> > > API's and structures not only used by the dmaengine driver's but
> > > also used by the various IP's (Ex: Ethernet driver and SRIO driver
> > > these drivers are under development).For example the Ethernet driver
> > > is resides under drivers/net/ethernet but it needs to set some
> > > specific configuration parameters of the dma that's why created a
> > > separate header file for the h/w configurable parameters.
> >
> > That is a bug in the ethernet driver, and we should not merge such code.
> >
> > Please fix those drivers before submitting them, so they don't rely on
> > additional interfaces beyond what the DMA engine API provides.
> >
> > If you need something that the common interface is missing, you can
> > send a patch to extend the dmaengine core driver, but more likely it
> > already does what you need and you are just not using it right.
> >
>
> Sorry for the delay in the reply.
> We need that header file in the include/linux/ directory for various
> reasons.
>
> As you know the Xilinx DMA's have a set of configurable parameters which
> we expect the DMA users to take advantage of.
>
> For example:
> For Axi DMA we have the following parameters that we expect to be
> commonly used.
> Coalesce count --> Used to configure the coalesce value.
> Delay timer ---> Used to set the delay value.
>
> We expect the Xilinx AXI Ethernet driver to use the Axi DMA driver in near
> furture. If so, using ethtool, we expect the driver users to play with the
> above parameters to do performance tuning.
>
> Hence AxiDMA driver must expose means to change coalese count or delay
> timer.
>
> Similarly For Axi VDMA we have the following parameters that will be used
> by the users of this driver.
> hsize --> Used to configure number of bytes per line.
> vsize -->Number of lines per frame.
> stride --> Number of bytes per line.
>
>
> Earlier in the driver we are embedding dma_slave_config into custom
> structs But Lars suggested to modify it. please refer to the below thread for
> more details.
> http://www.spinics.net/lists/dmaengine/msg00010.html
>
> And later we thought of creating a separate private member in
> dma_slave_config for sharing additional configuration between slave
> device and dma engine Or a new dma_ctrl_cmd like
> FSLDMA_EXTERNAL_START(http://www.kernelhub.org/?msg=405535&p=2 )
>
> Finally Vinod was ok with the existing suggestion so we dropped the above
> thought.
>
> @Vinod : Could you please comment on this.

Ping ?

Regards,
Kedar.

>
> Regards,
> Kedar.
>
> > Arnd



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