From: Arnd Bergmann <arnd@arndb.de>
To: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: linux-arm-kernel@lists.infradead.org,
Vinod Koul <vinod.koul@intel.com>,
Mark Rutland <mark.rutland@arm.com>,
devicetree@vger.kernel.org, Russell King <linux@arm.linux.org.uk>,
linux-kernel@vger.kernel.org, Sandeep Nair <sandeep_n@ti.com>,
Grant Likely <grant.likely@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
dmaengine@vger.kernel.org
Subject: Re: [PATCH] dma: Add Keystone Packet DMA Engine driver
Date: Tue, 18 Mar 2014 17:40:11 +0100 [thread overview]
Message-ID: <201403181740.11693.arnd@arndb.de> (raw)
In-Reply-To: <532872AD.2090804@ti.com>
On Tuesday 18 March 2014, Santosh Shilimkar wrote:
>
> On Tuesday 18 March 2014 11:38 AM, Arnd Bergmann wrote:
> > On Tuesday 18 March 2014 20:54:44 Vinod Koul wrote:
> >> On Mon, Mar 17, 2014 at 03:37:47PM -0400, Santosh Shilimkar wrote:
> >>>>> To simplify this bit more, you can think of this as DMA channels, flows
> >>>>> are allocated and DMA channels are enabled by DMA engine and they remains
> >>>>> enabled always as long as the channel in use. Enablling dma channel
> >>>>> actually don't start the DMA transfer but just sets up the connection/pipe
> >>>>> with peripheral and memory and vice a versa.
> >>>>>
> >>>>> All the descriptor management, triggering, sending completion interrupt or
> >>>>> hardware signal to DMAEngine all managed by centralised QMSS.
> >>>>>
> >>>>> Actual copy of data is still done by DMA hardware but its completely
> >>>>> transparent to software. DMAEngine hardware takes care of that in the
> >>>>> backyard.
> >>>> So you will use the dmaengine just for setting up the controller. Not for actual
> >>>> transfers. Those would be governed by the QMSS, right?
> >>>>
> >>> Correct.
> >>>
> >>>> This means that someone expecting to use dmaengine API will get confused about
> >>>> this and doing part (alloc) thru dmaengine and rest (transfers) using some other
> >>>> API. This brings to me the design approach, does it really make sense creating
> >>>> dmaengine driver for this when we are not fully complying to the API
> >>>>
> >>> Thats fair. The rationale behind usage of DMEngine was that its the closest
> >>> available subsystem which can be leveraged for this hardware. We can
> >>> pretty much use all the standard DMAEngine device tree parsing as well as
> >>> the config API to setup DMAs.
> >>>
> >>> I think you made your stand clear, just to confirm, you don't prefer this
> >>> driver to be a DMAEngine driver considering it doesn't fully complying to
> >>> the APIs. We could document the deviation of 'transfer' handling to avoid
> >>> any confusion.
> >> Yup, a user will just get confused as the driver doenst conform the dmaengine
> >> API. Unless someone comes up witha strong argument on why it should be
> >> dmaengine driver and what befits we see form such a model, i would like a
> >> damengine driver to comply to standard API and usage.
> >
> > I think it would be possible to turn the QMSS driver into a library and have
> > the packet DMA code use the proper dmaengine API by calling into that code.
> >
> > The main user of packet DMA (the ethernet driver) would however still have
> > to call into QMSS directly, so I'm not sure if it's worth the effort.
> >
> Its not. Am going to move this driver along with QMSS which is one
> of the options we discussed.
Ok, fair enough. Looking forward to the patches.
Arnd
next prev parent reply other threads:[~2014-03-18 16:41 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-28 22:56 [PATCH] dma: Add Keystone Packet DMA Engine driver Santosh Shilimkar
2014-02-28 23:14 ` Arnd Bergmann
2014-02-28 23:44 ` Santosh Shilimkar
2014-03-05 2:26 ` Santosh Shilimkar
2014-03-03 9:34 ` Shevchenko, Andriy
2014-03-11 10:23 ` Vinod Koul
2014-03-11 19:50 ` Santosh Shilimkar
2014-03-12 16:00 ` Vinod Koul
2014-03-12 21:16 ` Santosh Shilimkar
2014-03-17 4:42 ` Vinod Koul
2014-03-17 19:37 ` Santosh Shilimkar
2014-03-18 15:24 ` Vinod Koul
2014-03-18 15:38 ` Arnd Bergmann
2014-03-18 15:51 ` Vinod Koul
2014-03-18 16:22 ` Santosh Shilimkar
2014-03-18 16:40 ` Arnd Bergmann [this message]
2014-03-18 16:19 ` Santosh Shilimkar
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