From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH V2] dma: tegra: register as an OF DMA controller
Date: Wed, 04 Dec 2013 10:09:39 -0700 [thread overview]
Message-ID: <529F61D3.3030104@wwwdotorg.org> (raw)
In-Reply-To: <201312040222.03604.arnd@arndb.de>
On 12/03/2013 06:22 PM, Arnd Bergmann wrote:
> On Tuesday 03 December 2013, Stephen Warren wrote:
>> On 11/29/2013 02:08 PM, Arnd Bergmann wrote:
>
>>> Can you try coming up with a different method to achieve the same
>>> where you use a different helper from the driver specific xlate
>>> function that does not require a callback?
>>>
>>> I think dma_get_slave_channel is great if you have one channel per
>>> request line and you can directly look up the channel from the
>>> DT data, but it is not good if you have pick a channel and work
>>> around the race.
>>
>> Hmm. Can you take a look at "[PATCH V4] dma: add
>> dma_get_any_slave_channel(), for use in of_xlate()" at the link below.
>> It still implements this via xlate, but I don't see any benefit in
>> making drivers use a different API to request slave channels based on
>> how the DMA controller works.
>>
>> http://lkml.org/lkml/2013/11/26/408
>
> Yes, I think that is good. I can think of a few variations of that
> that I would prefer slightly over your code, but it's essentially
> what I had in mind and I'm fine with that version getting merged
> as well. Here are my ideas for further improvements, I'll leave
> it up to you and the dmaengine maintainers to decide what to do
> about them:
>
> * Rather than calling private_candidate(), open-code the part you
> need and remove the pointless dma_cap_mask comparison:
>
> err = -EBUSY;
> list_for_each_entry(chan, &dev->channels, device_node) {
> if (!chan->client_count) {
> err = dma_chan_get(chan);
> break;
> }
> }
Lars-Peter had specifically suggested to call private_candidate(). Lars,
what do you think about open-coding this? Arnd's suggestion would skip
the DMA_PRIVATE checking that private_candidate() does, and I'm not sure
what the implications of that would be.
> * Merge the new function with dma_get_slave_channel(). They really
> do different things, but I think it still makes sense as an API
> to require to always pass the dma_device pointer, and drivers
> that want to get an arbitrary channel can just pass NULL as the
> channel pointer.
I suppose one could do that, although the two operations seem pretty
semantically different to me, such that merging them doesn't seem correct.
next prev parent reply other threads:[~2013-12-04 17:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-25 21:53 [PATCH V2] dma: tegra: register as an OF DMA controller Stephen Warren
2013-11-25 22:09 ` Arnd Bergmann
2013-11-25 22:30 ` Stephen Warren
2013-11-25 23:09 ` Dan Williams
2013-11-25 23:14 ` Stephen Warren
2013-11-26 1:13 ` Dan Williams
2013-11-29 21:08 ` Arnd Bergmann
2013-12-03 17:52 ` Stephen Warren
2013-12-04 1:22 ` Arnd Bergmann
2013-12-04 17:09 ` Stephen Warren [this message]
2013-12-04 17:18 ` Lars-Peter Clausen
2013-12-06 21:16 ` Dan Williams
2013-12-06 22:19 ` Arnd Bergmann
2013-11-29 14:17 ` Thierry Reding
2013-12-03 17:59 ` Stephen Warren
2013-12-04 8:29 ` Thierry Reding
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