From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
To: Vinod Koul <vinod.koul@intel.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel()
Date: Tue, 6 Mar 2012 14:03:36 +0100 (CET) [thread overview]
Message-ID: <Pine.LNX.4.64.1203061339330.9300@axis700.grange> (raw)
In-Reply-To: <1331035739.24656.201.camel@vkoul-udesk3>
On Tue, 6 Mar 2012, Vinod Koul wrote:
> On Tue, 2012-03-06 at 09:53 +0100, Guennadi Liakhovetski wrote:
> > Hi Vinod
> >
> > Thanks for your review.
> >
> > On Tue, 6 Mar 2012, Vinod Koul wrote:
> >
> > > On Fri, 2012-03-02 at 14:21 +0100, Guennadi Liakhovetski wrote:
> > > > Hi Vinod
> > > >
> > > > On Wed, 1 Feb 2012, Guennadi Liakhovetski wrote:
> > > sorry I thought I had replied, but looks like it got missed!
> > > >
> > > > > When performing slame DMA some dmaengine drivers need additional data from
> > > typo ^^^^^^^^^
> > > > > client drivers to find out, whether they can support that specific client
> > > > > and to configure the DMA channel for it. This additional data has to be
> > > > > supplied by client drivers during channel allocation, i.e., with the
> > > > > __dma_request_channel() function. This patch adds a new
> > > > > struct dma_slave_desc with some basic data in it, further this struct can
> > > > > be embedded in hardware-specific types to supply any auxiliary
> > > > > configuration.
> > > counter arguing shouldn't the client drivers find out of the channel
> > > requested is capable or not, that can be alternate approach as well.
> > > That way people implement this in the filer functions and find if this
> > > is the channel we need rather than dmac finding out if it can service
> > > the client or not.
> >
> > How shall clients find this out? This is system- and DMAC-specific, this
> > has nothing to do with the client functionality. The proposed approach is:
> >
> > * a client driver (MMC, USB, anything else) is capable to use DMA uses the
> > standard dmaengine API to transfer the data
> >
> > * if the platform, where it's running, is supplying any auxiliary data,
> > that it has to pass to the DMAC driver, it can do so, without getting
> > involved in the details, just passing a pointer
> >
> > * the most natural location to do this is IMHO when requesting a DMA
> > channel
> and in that case why do you need the new parameters to be passed back in
> filter function. What is the role of filter in this case ?
Sorry, who said I needed them? No changes are required to the filter
function. As for its role - don't know, I didn't design it:-) In my case
the filter will essentially become a "return true" dummy, respectively, it
can simply be omitted. In general, I can hardly imagine a situation,
where, say, an MMC driver would have internal knowledge about DMA channels
on the system, allowing it to select a suitable one... So, I'm really not
sure what it is for. Good, that it is at least optional. Maybe it can be
deprecated with time.
> > Now, on sh-mobile platforms you can realistically have around 5 DMAC
> > instances with 2 or 6 channels each, of which, say, 3 controllers are
> > suitable for MMC and 2 are not. How shall the filter function find this
> > out? Call some ugly platform callback? Traverse some platform-specific
> > lists? Or use a fixed channel, thus significantly reducing flexibility?
> > Sorry, none of these options seems very attractive to me.
> well you can counter argue that dmac does not have this information
> either.
But the DMAC is certainly a better match for making channel-selection
decisions.
> Bigger question is who knows about this mapping and how do we
> incorporate this mapping into channel allocation
The platform does. And this knowledge has to be passed to the relevant
driver. But I think it's the DMAC driver, that is relevant, not the client
driver. The platform would supply information like
DMAC #1
channel #1
(can be used for) device #1
device #2
...
channel #2
...
...
And I don't think, it would be reasonable to let every slave driver use
this information. These lists can also be optimised for specific
platforms. E.g., on some sh-mobile SoCs you have two DMAC types. One of
them can serve devices from list A on any channel, the other one - from
list B. So, all you have to do, is to reference either A or B from your
DMAC platform data. Whereas doing a reverse mapping: for each (potential)
DMA user reference a list of channels, that it can use - would be really
clumsy.
> > > Frankly I prefer former model, as that way dmacs will present channel
> > > capabilities, and clients can use as they deem fit.
> > > > >
> > > > > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
next prev parent reply other threads:[~2012-03-06 13:03 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-01 15:26 [PATCH/RFC] dmaengine: add a slave parameter to __dma_request_channel() Guennadi Liakhovetski
2012-03-02 13:21 ` Guennadi Liakhovetski
2012-03-06 8:30 ` Vinod Koul
2012-03-06 8:53 ` Guennadi Liakhovetski
2012-03-06 12:08 ` Vinod Koul
2012-03-06 13:03 ` Guennadi Liakhovetski [this message]
2012-03-07 6:28 ` Vinod Koul
2012-03-07 9:18 ` Guennadi Liakhovetski
2012-03-07 9:30 ` Russell King - ARM Linux
2012-03-07 9:55 ` Linus Walleij
2012-03-07 10:02 ` Guennadi Liakhovetski
2012-03-07 10:31 ` Russell King - ARM Linux
2012-03-07 12:30 ` Guennadi Liakhovetski
2012-03-07 12:45 ` Guennadi Liakhovetski
2012-03-07 12:46 ` Russell King - ARM Linux
2012-03-07 13:49 ` Guennadi Liakhovetski
2012-03-07 14:26 ` Russell King - ARM Linux
2012-03-07 15:44 ` Guennadi Liakhovetski
2012-03-07 16:27 ` Russell King - ARM Linux
2012-03-07 18:21 ` Guennadi Liakhovetski
2012-03-08 6:30 ` Vinod Koul
2012-03-08 10:16 ` Guennadi Liakhovetski
2012-03-08 10:55 ` Vinod Koul
2012-03-08 11:22 ` Guennadi Liakhovetski
2012-03-08 11:34 ` Vinod Koul
2012-03-08 12:58 ` Vinod Koul
2012-03-08 13:18 ` Guennadi Liakhovetski
2012-03-09 9:21 ` Vinod Koul
2012-03-09 9:24 ` Guennadi Liakhovetski
2012-03-09 9:39 ` Vinod Koul
2012-03-09 12:20 ` Guennadi Liakhovetski
2012-03-09 14:07 ` Russell King - ARM Linux
2012-03-09 14:15 ` Guennadi Liakhovetski
2012-03-12 2:47 ` Vinod Koul
2012-03-12 19:47 ` Linus Walleij
2012-03-16 9:36 ` Guennadi Liakhovetski
2012-03-16 10:16 ` Linus Walleij
2012-03-16 10:31 ` Russell King - ARM Linux
2012-03-16 11:09 ` Guennadi Liakhovetski
2012-03-16 14:11 ` Linus Walleij
2012-03-16 14:28 ` Guennadi Liakhovetski
2012-03-30 5:44 ` Linus Walleij
2012-03-30 6:40 ` Guennadi Liakhovetski
2012-03-30 10:38 ` Russell King - ARM Linux
2012-04-03 20:36 ` Linus Walleij
2012-04-03 20:44 ` Linus Walleij
2012-04-12 21:33 ` Guennadi Liakhovetski
2012-04-12 23:48 ` Russell King - ARM Linux
2012-03-30 10:29 ` Russell King - ARM Linux
2012-03-30 10:40 ` Guennadi Liakhovetski
2012-03-30 10:43 ` Russell King - ARM Linux
2012-03-19 11:58 ` Vinod Koul
2012-03-30 10:25 ` Russell King - ARM Linux
2012-03-19 11:39 ` Vinod Koul
2012-03-19 11:37 ` Vinod Koul
2012-03-19 11:47 ` Guennadi Liakhovetski
2012-03-19 13:34 ` Vinod Koul
2012-03-19 13:38 ` Guennadi Liakhovetski
2012-03-19 14:00 ` Vinod Koul
2012-03-19 14:09 ` Guennadi Liakhovetski
2012-03-19 14:22 ` Vinod Koul
2012-03-19 14:45 ` Guennadi Liakhovetski
2012-03-19 16:20 ` Vinod Koul
2012-03-19 16:32 ` Guennadi Liakhovetski
2012-03-20 7:11 ` Vinod Koul
2012-03-08 11:46 ` Linus Walleij
2012-03-08 12:36 ` Guennadi Liakhovetski
2012-03-07 16:31 ` Linus Walleij
2012-03-07 16:20 ` Linus Walleij
2012-03-07 9:46 ` Linus Walleij
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