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SubjectRe: [PATCH v4 1/8] dmaengine: of_dma: Support for DMA routers
On Thu, Apr 09, 2015 at 11:24:58AM +0300, Peter Ujfalusi wrote:
> On 04/08/2015 06:42 PM, Maxime Ripard wrote:
> >> ---
> >> Documentation/devicetree/bindings/dma/dma.txt | 28 +++++++++
> >> drivers/dma/dmaengine.c | 7 +++
> >> drivers/dma/of-dma.c | 86 +++++++++++++++++++++++++++
> >> include/linux/dmaengine.h | 17 ++++++
> >> include/linux/of_dma.h | 21 +++++++
> >> 5 files changed, 159 insertions(+)
> >
> > Can that be moved to a header / C file of its own?
> >
> > There's a lot of various code already in dmaengine.h and dmaengine.c,
> > it would be really great to avoid adding more random stuff in there.
>
> This patch adds the core support for DMA signal routers. It adds
> fairly small amount of generic code to the core to achieve this. I
> don't think it would be better to create let's say of-dma-router.c
> and .h just for this and export functions from of-dma.c to be used
> outside of the file.

A lot of "a fairly small amount of generic code" has been added over
time, and we ended up in the current situation.

It's a bit sad if we just end up moving this just after it got merged,
especially if it doesn't have any kind of dependency on any of the
core function.

> >> +int of_dma_router_register(struct device_node *np,
> >> + void *(*of_dma_route_allocate)
> >> + (struct of_phandle_args *, struct of_dma *),
> >> + struct dma_router *dma_router)
> >> +{
> >> + struct of_dma *ofdma;
> >> +
> >> + if (!np || !of_dma_route_allocate || !dma_router) {
> >> + pr_err("%s: not enough information provided\n", __func__);
> >> + return -EINVAL;
> >> + }
> >> +
> >> + ofdma = kzalloc(sizeof(*ofdma), GFP_KERNEL);
> >> + if (!ofdma)
> >> + return -ENOMEM;
> >
> > Is that expected that you allocate through kzalloc, but never have a
> > matching free function implemented?
>
> The free is via the of_dma_router_free() in case the router is removed
> runtime, which is unlikely to happen since it will cause all DMA request to fail.

Ok.

> >> diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
> >> index 56bc026c143f..734e449f87c1 100644
> >> --- a/include/linux/of_dma.h
> >> +++ b/include/linux/of_dma.h
> >> @@ -23,6 +23,9 @@ struct of_dma {
> >> struct device_node *of_node;
> >> struct dma_chan *(*of_dma_xlate)
> >> (struct of_phandle_args *, struct of_dma *);
> >> + void *(*of_dma_route_allocate)
> >> + (struct of_phandle_args *, struct of_dma *);
> >> + struct dma_router *dma_router;
> >
> > I don't really see why this is really tied to the device tree.
>
> The signal router is not a DMA device, it is represented in the device tree
> and the code will do the needed translation, which is transparent for the DMA
> clients and also for the DMA controllers. Neither should know about the signal
> router.

Yeah, I got that part, and we do agree on that.

> Similar translation can be done for ACPI.

But this argument is exactly why it shouldn't be tied to the device
tree. We wouldn't like to re-do all this all over again for ACPI,
while your code seems to just handle that very well, wouldn't we?

> > Couldn't we use the device_alloc_chan_resources to do that?
>
> Not really. The router itself is not a DMA controller. The routing
> need to be configured before the device_alloc_chan_resources can be
> called for the real DMA controller. The signal router (core part +
> the HW driver) need to prepare the route and do the translation so
> the filter function of the DMA driver can validate the translated
> request.

Ah, yes, hence why you need a custom xlate function. Got it, thanks!

Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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