Messages in this thread | | | Subject | Re: [PATCH V2 1/2] Documentation: DT: Add binding documentation for NVIDIA ADMA | From | Stephen Warren <> | Date | Fri, 9 Oct 2015 09:26:01 -0600 |
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On 10/09/2015 04:20 AM, Jon Hunter wrote: > > On 08/10/15 15:27, Stephen Warren wrote: >> On 10/08/2015 03:58 AM, Jon Hunter wrote: > > [snip] > >>> That's fine. From my perspective I don't have a strong objection either >>> way, however, I can see that given that the name indicates rx or tx, >>> then the direction in the binding could be seen as redundant. >>> >>> So to confirm you are happy with the client bindings being as follows? >>> >>> tegra_admaif: admaif@0x702d0000 { >>> ... >>> dmas = <&adma 1>, <&adma 1>, <&adma 2>, <&adma 2>, >>> <&adma 3>, <&adma 3>, <&adma 4>, <&adma 4>, >>> <&adma 5>, <&adma 5>, <&adma 6>, <&adma 6>, >>> <&adma 7>, <&adma 7>, <&adma 8>, <&adma 8>, >>> <&adma 9>, <&adma 9>, <&adma 10>, <&adma 10>; >>> dma-names = "rx1", "tx1", "rx2", "tx2", "rx3", "tx3", >>> "rx4", "tx4", "rx5", "tx5", "rx6", "tx6", >>> "rx7", "tx7", "rx8", "tx8", "rx9", "tx9", >>> "rx10", "tx10"; >>> ... >>> }; >> >> Yes, that looks good for the client binding. > > One more clarifying question ... should the xlate verify that no other > dma channel is using the same hardware request signal? > > I understand that typically the xlate decodes the binding to get the > channel info, but because this is invoked by dmaengine while allocating > a channel, I was wondering if we should prevent dmaengine allocating > more than one channel to be used with the same hardware request? If so, > then passing the direction to the xlate would be necessary (so I can > determine in the xlate that no one else is currently using this, which > is what I currently do). > > Alternatively, I could check that no one else is using the request > signal at a later when the transfer is being prepared.
I think that handling this at prepare/usage time is probably most appropriate. That is the time when the resource conflict /actually/ occurs.
The only time when two clients would be given the same DMA request signal is if there are multiple different drivers that can DMA into the same FIFO in a time-multiplexed fashion. That seems pretty unlikely off the top of my head, but I don't think we want to actively ban that, in case we come up with a cunning use-case for it.
> If you are wondering why I am worried about this, I my mind I think that > the driver should be robust enough to check for conflicts in the request > signals used by the various channels.
Sure, makes sense.
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