From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
To: Vinod Koul <vinod.koul@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org,
Magnus Damm <magnus.damm@gmail.com>,
Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
linux-mmc@vger.kernel.org, alsa-devel@alsa-project.org,
linux-serial@vger.kernel.org, Paul Mundt <lethal@linux-sh.org>
Subject: Re: [PATCH 1/7 v2] dmaengine: add a simple dma library
Date: Tue, 31 Jan 2012 09:59:36 +0100 (CET) [thread overview]
Message-ID: <Pine.LNX.4.64.1201310746470.31226@axis700.grange> (raw)
In-Reply-To: <1327992090.1527.116.camel@vkoul-udesk3>
Hi Vinod
Thanks for your reply.
On Tue, 31 Jan 2012, Vinod Koul wrote:
> On Mon, 2012-01-30 at 10:34 +0100, Guennadi Liakhovetski wrote:
> > > I don't still comprehend the need for a library on top of dmaengine
> > > which gain is just a library between clients and dmacs. Surely we don't
> > > want to write another abstraction on top of one provided?
> > >
> > > If the question is to handle scatter-gather even if the hardware doesn't
> > > have the capability, then why don't add that in dmaengine itself rather
> > > than one more layer?
> >
> > Well, yes, adding new abstraction layers is always a decision, that has to
> > be well justified. In this case it does at least make the life easier for
> > two sh-mobile drivers: shdma and the new SUDMAC driver.
> >
> > However, I did name the library in a generic way without reference to sh,
> > assuming, that it might with time become useful for other architectures
> > too. The reasons why I prefered to keep it as an optional addition to
> > dmaengine core, instead of tightly integrating it with it are, that (1) I
> > did not want to add useless code to drivers, that do not need it,
> So are we sure that only sh-mobile drivers need this capablity?
If I was sure about that, I'd call the library shmobile-dma or something
similar:-)
> Btw does you hardware only support single transfers and no sg support,
Well, the controller does have some repeat- and reload-modes, but they are
currently not supported by the driver and from the documentation I cannot
easily understand, how useful those modes could be to implement SG.
> would this remain the same in future?
Who knows?...
> > (2) I am
> > not sure if and when this library will become useful for other drivers:
> > apart from sh I am only familiar with one more dmaengine driver:
> > ipu/ipu_idmac.c, and that one supports scatter-gather lists in a limited
> > way and has some further peculiarities, that would likely make it a bad
> > match for the simple DMA library,
> typically the dmacs will support this in some form or other, so your
> point is valid :)
> > (3) keeping it separate makes its
> > further development easier.
> >
> > OTOH, I'm certainly fine with a tighter library integration with the
> > dmaengine core. I think, it still would be better to keep it in a separate
> > file and only build it if needed, right? This woult also simplify code
> > debugging and further development. I can remove the "simple" notation,
> > which does make it look like an additional abstraction layer, and replace
> > it with, say, sgsoft (scatter-gather software implementation)?
> that would be more apt :)
> > A more
> > interesting question is what to do with struct dma_simple_dev, struct
> > dma_simple_chan, struct dma_simple_desc, that embed struct dma_device,
> > struct dma_chan and struct dma_async_tx_descriptor respectively. I don't
> > think we want to merge all the additions from those wrapping structs back
> > into their dmaengine counterparts?
> Sure they should be kept separate. I like the wrapping, this keeps it
> simple.
> >
> > How would you like to do this? Don't you think, it would be good to allow
> > both: either implement a dmaengine driver directly, exactly as all drivers
> > are doing now, or use the additional helper library for suitable (simple)
> > hardware types? I see it similar to I2C, where you either implement an I2C
> > driver directly, or you use the bitbanging abstraction for simpler
> > hardware.
> I think it would be good to have both, this can be used by folks who
> don't have sg support available.
Ok, so, should I just rename the driver to sgsoft? Is this the only
change, that you'd like to see?
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
next prev parent reply other threads:[~2012-01-31 8:59 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-26 14:56 [PATCH 0/7 v2] extract a simple dmaengine library from shdma.c Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 1/7 v2] dmaengine: add a simple dma library Guennadi Liakhovetski
2012-01-26 17:34 ` [alsa-devel] " Sascha Hauer
2012-01-26 21:07 ` Guennadi Liakhovetski
2012-01-27 8:37 ` Shimoda, Yoshihiro
2012-01-27 8:48 ` Guennadi Liakhovetski
2012-01-31 11:03 ` Shimoda, Yoshihiro
2012-02-01 0:52 ` Guennadi Liakhovetski
2012-02-01 2:47 ` Shimoda, Yoshihiro
2012-02-02 22:19 ` Guennadi Liakhovetski
2012-02-03 8:47 ` Shimoda, Yoshihiro
2012-02-03 10:21 ` Guennadi Liakhovetski
2012-02-03 15:43 ` [PATCH/RFC] usb: fix renesas_usbhs to not schedule in atomic context Guennadi Liakhovetski
2012-02-05 14:54 ` Felipe Balbi
2012-02-06 10:11 ` Guennadi Liakhovetski
2012-02-06 10:31 ` Felipe Balbi
2012-02-06 8:52 ` Shimoda, Yoshihiro
2012-01-30 8:32 ` [PATCH 1/7 v2] dmaengine: add a simple dma library Vinod Koul
2012-01-30 9:34 ` Guennadi Liakhovetski
2012-01-31 6:41 ` Vinod Koul
2012-01-31 8:59 ` Guennadi Liakhovetski [this message]
2012-02-01 5:38 ` Vinod Koul
2012-02-03 16:38 ` Guennadi Liakhovetski
2012-02-06 2:54 ` Vinod Koul
2012-02-06 9:53 ` Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 2/7 v2] dma: shdma: prepare for simple DMA conversion Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 3/7 v2] mmc: sh_mmcif: remove unneeded struct sh_mmcif_dma, prepare for simple DMA Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 4/7 v2] mmc: sh_mobile_sdhi: prepare for conversion to " Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 5/7 v2] serial: sh-sci: " Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 6/7 v2] ASoC: SIU: " Guennadi Liakhovetski
2012-02-06 2:33 ` Vinod Koul
2012-02-06 9:11 ` Guennadi Liakhovetski
2012-01-26 14:56 ` [PATCH 7/7 v2] dma: shdma: convert to the simple DMA library Guennadi Liakhovetski
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