From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V3 1/2] of: Add generic device tree DMA helpers
Date: Fri, 15 Jun 2012 08:40:32 +0000 [thread overview]
Message-ID: <201206150840.33347.arnd@arndb.de> (raw)
In-Reply-To: <4FDA05A4.5090301@ti.com>
On Thursday 14 June 2012, Jon Hunter wrote:
>
> On 06/14/2012 06:48 AM, Arnd Bergmann wrote:
> > On Wednesday 13 June 2012, Jon Hunter wrote:
> >> So in that case, I don't see why the first cell after the phandle could
> >> not be an index which could be either a direction or request-id and then
> >> the next cell after that be a secondary match variable.
> >>
> >> So simple case with just a index (either req-id or direction) ...
> >>
> >> dmas = <&dmac0 index>
> >>
> >> More complex case ...
> >>
> >> dmas = <&dmac0 index match>
> >>
> >> For example, for OMAP index = req-id and match = direction ...
> >>
> >> dmas = <&dmac0 req-id direction>
> >>
> >> Or am I way off the page?
> >
> > The intention was instead to remove the need for the /index/ in those
> > cases, because having a client-specific index in here makes it inconsistent
> > with other similar bindings (reg, interrupts, gpios, ...) that people
> > are familiar with. They use an implicit index by counting the
> > fields in the respective properties.
>
> So maybe "index" was not the right term to use here. What I meant was
> that this is really the req/chan-id associated with this device. It is
> not an arbitrary index that in turn gets resolved into the req-id. So in
> other words, just like gpio where you have the gpio number, here you
> have the dma req-id.
Ok, we're on the same page then.
I got confused because you were quoting Stephen's example of
multiple dmacs:
dmas = <0 &dmac1 xxx 0 &dmac2 zzz 1 &dmac1 yyy>;
which used an aribitrary slave-side index (0, 1), the dmaengine phandle
and the dmaengine specific request id (xxx,yyy,zzz).
Leaving out the index means that we require at least one of "dma-names"
strings or adding the direction.
> > The existing method we have for avoiding index numbers is to use
> > named fields, like
> >
> > dmas = <&dmac0 matchA>, <dmac1 matchB>, <dmac2 matchC>;
> > dma-names = "rx", "rx", "tx";
> >
> > This is similar to how we use named interrupt and mmio resources, but
> > it requires that we always request the dma lines by name, which is
> > slightly more complex than we might want it to be.
>
> Ok, but how do you get the req-id from the above binding? Doesn't it
> need to be stored there somewhere even for the most simplest case? Or
> are you saying that in this case you are just returning a name and the
> dma driver resolves that into a req-id?
the req-id is what I called matchA, matchB, matchC here, it could be
a set of multiple cells, the number of which gets determined by the
dmaengine's #dma-cells property.
> > Because the vast majority of cases just use a single channel, or one
> > channel per direction, my idea was to encode the direction in the
> > dmas property, which lets us request a dma channel by direction from
> > the driver side, without explicitly encoding the name.
>
> Yes, thats fine and so the direction is really the match criteria in
> this case.
No, it's not :(
> > This would let us handle the following cases very easily:
> >
> > 1. one read-write channel
> >
> > dmas = <&dmac 0x3 match>;
>
> Where 0x3 is the req-id? Just to confirm ;-)
>
> Why not have match after the phandle to be consistent with the simple
> example using name fields above?
The 0x3 is the direction, 1 for read, 2 for write, and 3 for read-write
in this example. Sorry for being unclear.
The direction has to come before the dma-engine specific request ID
data so that the common code can interpret it, while the variable-length
data after it is only interpreted by the dmaengine driver.
Arnd
next prev parent reply other threads:[~2012-06-15 8:40 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-30 21:17 [PATCH V3 1/2] of: Add generic device tree DMA helpers Jon Hunter
2012-05-03 22:26 ` Stephen Warren
2012-05-03 23:25 ` Russell King - ARM Linux
2012-05-04 12:39 ` Arnd Bergmann
2012-05-04 15:06 ` Jon Hunter
2012-05-04 15:14 ` Russell King - ARM Linux
2012-05-04 18:21 ` Stephen Warren
2012-05-04 19:19 ` Jon Hunter
2012-05-04 6:56 ` Jassi Brar
2012-05-04 15:17 ` Jon Hunter
2012-05-04 19:01 ` Jassi Brar
2012-05-04 19:23 ` Arnd Bergmann
2012-05-05 17:10 ` Jassi Brar
2012-05-07 15:53 ` Stephen Warren
2012-05-07 17:19 ` Jassi Brar
2012-05-08 16:35 ` Stephen Warren
2012-05-08 19:09 ` Jassi Brar
2012-05-09 12:30 ` Arnd Bergmann
2012-05-09 19:10 ` Stephen Warren
2012-05-09 21:38 ` Jassi Brar
2012-05-10 17:00 ` Stephen Warren
2012-05-10 19:59 ` Jassi Brar
2012-05-11 19:28 ` Stephen Warren
2012-05-11 21:06 ` Jassi Brar
2012-05-11 23:51 ` Stephen Warren
2012-05-12 13:40 ` Jassi Brar
2012-05-16 1:05 ` Jon Hunter
2012-05-17 13:18 ` Russell King - ARM Linux
2012-05-07 17:21 ` Arnd Bergmann
2012-05-16 1:11 ` Jon Hunter
2012-05-16 12:37 ` Jassi Brar
2012-05-16 13:15 ` Jon Hunter
2012-05-16 15:44 ` Stephen Warren
2012-05-16 16:04 ` Jon Hunter
2012-05-16 16:01 ` Jon Hunter
2012-05-16 16:15 ` Stephen Warren
2012-05-16 16:22 ` Jassi Brar
2012-05-16 17:09 ` Jon Hunter
2012-05-16 19:42 ` Arnd Bergmann
2012-05-16 21:16 ` Jassi Brar
2012-05-17 19:32 ` Stephen Warren
2012-05-18 17:12 ` Jassi Brar
2012-05-18 21:04 ` Arnd Bergmann
2012-05-16 23:59 ` Stephen Warren
2012-05-17 4:05 ` Jassi Brar
2012-05-18 20:49 ` Arnd Bergmann
2012-05-18 21:07 ` Stephen Warren
2012-05-18 21:43 ` Arnd Bergmann
2012-05-18 22:20 ` Stephen Warren
2012-05-19 8:44 ` Arnd Bergmann
2012-05-21 17:33 ` Stephen Warren
2012-05-21 18:18 ` Arnd Bergmann
2012-05-21 20:32 ` Stephen Warren
2012-06-08 19:04 ` Jon Hunter
2012-06-09 0:04 ` Arnd Bergmann
2012-06-13 22:32 ` Jon Hunter
2012-06-14 4:45 ` Jassi Brar
2012-06-14 11:48 ` Arnd Bergmann
2012-06-14 15:39 ` Jon Hunter
2012-06-15 8:40 ` Arnd Bergmann [this message]
2012-06-22 22:52 ` Jon Hunter
2012-06-22 23:12 ` Russell King - ARM Linux
2012-06-25 16:51 ` Jon Hunter
2012-06-25 18:04 ` Vinod Koul
2012-06-25 20:30 ` Arnd Bergmann
2012-06-26 9:40 ` Vinod Koul
2012-06-26 14:59 ` Arnd Bergmann
2012-06-26 17:50 ` Vinod Koul
2012-06-26 20:27 ` Arnd Bergmann
2012-06-27 13:45 ` Vinod Koul
2012-06-27 15:20 ` Arnd Bergmann
2012-07-13 6:45 ` Vinod Koul
2012-07-13 21:52 ` Guennadi Liakhovetski
2012-07-17 19:24 ` Arnd Bergmann
2012-07-20 4:00 ` Vinod Koul
2012-07-20 8:39 ` Arnd Bergmann
2012-07-20 9:37 ` Vinod Koul
2012-07-24 19:07 ` Jon Hunter
2012-07-24 19:27 ` Arnd Bergmann
2012-07-26 6:42 ` Vinod Koul
2012-07-26 7:14 ` Arnd Bergmann
2012-07-26 11:28 ` Vinod Koul
2012-07-26 15:53 ` Jon Hunter
2012-07-31 11:06 ` Vinod Koul
2012-07-26 17:43 ` Jon Hunter
2012-07-31 11:12 ` Vinod Koul
2012-08-01 20:43 ` Jon Hunter
2012-08-03 9:55 ` Vinod Koul
2012-07-20 9:08 ` Robert Jarzmik
2012-07-20 9:41 ` Vinod Koul
2012-07-26 4:56 ` zhangfei gao
2012-07-23 21:29 ` Stephen Warren
2012-07-24 7:19 ` Arnd Bergmann
2012-07-24 16:04 ` Stephen Warren
2012-07-24 18:55 ` Arnd Bergmann
2012-07-24 12:54 ` Sergei Shtylyov
2012-07-06 11:36 ` Guennadi Liakhovetski
2012-07-06 15:28 ` Arnd Bergmann
2012-07-06 15:43 ` Guennadi Liakhovetski
2012-07-06 17:31 ` Arnd Bergmann
2012-07-06 21:01 ` Russell King - ARM Linux
2012-07-06 20:57 ` Russell King - ARM Linux
2012-07-06 22:49 ` Guennadi Liakhovetski
2012-07-13 6:51 ` Vinod Koul
2012-06-14 15:17 ` Guennadi Liakhovetski
2012-06-14 21:52 ` Jon Hunter
2012-06-15 8:41 ` Guennadi Liakhovetski
2012-06-15 9:00 ` Arnd Bergmann
2012-06-15 9:18 ` Guennadi Liakhovetski
2012-06-15 11:27 ` Arnd Bergmann
2012-06-15 16:11 ` Mitch Bradley
2012-06-16 6:56 ` Arnd Bergmann
2012-06-21 11:21 ` Guennadi Liakhovetski
2012-06-21 14:56 ` Arnd Bergmann
2012-05-17 13:22 ` Russell King - ARM Linux
2012-05-17 13:52 ` Mark Brown
2012-05-17 14:16 ` Russell King - ARM Linux
2012-05-16 16:16 ` Jassi Brar
2012-05-16 17:12 ` Jon Hunter
2012-05-16 17:24 ` Jassi Brar
2012-05-16 17:37 ` Jon Hunter
2012-05-16 17:46 ` Stephen Warren
2012-05-16 18:03 ` Jon Hunter
2012-05-04 15:22 ` Jon Hunter
2012-05-04 15:56 ` Arnd Bergmann
2012-05-04 17:19 ` Jon Hunter
2012-05-04 19:06 ` Arnd Bergmann
2012-05-04 19:26 ` Jon Hunter
2012-05-04 18:30 ` Stephen Warren
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