Re: [PATCH v2 1/2] dma: mmp_dma: add support for legacy transition

From: Robert Jarzmik
Date: Thu Feb 19 2015 - 14:54:16 EST

Daniel Mack <daniel@xxxxxxxxxx> writes:

> Hi Robert,
> Thanks for pushing this topic :)
> One minor nit:
>> +int mmp_pdma_toggle_reserved_channel(int legacy_channel)
>> +{
>> + if (legacy_unavailable & (1 << legacy_channel))
>> + return -EBUSY;
>> + legacy_reserved ^= 1 << legacy_channel;
>> + return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(mmp_pdma_toggle_reserved_channel);
> My concern is that if pxa_request_dma() is called more than once for
> whatever reason by a legacy implementation, the toggled bit mask might
> get out of sync.
This is not possible.
The first call to pxa_request_dma() sets dma_channels[i].name to a non-NULL
The second call to pxa_request_dma() cannot take the same i as
!dma_channels[i].name is not fullfilled.

> As we know exactly on the caller site what we want to achieve, let's make the
> API explicit with something like:
> int mmp_pdma_set_reserved_channel(int legacy_channel, bool reserved)
Even if I have no strong opinion about it, I'll let the patch as it is, unless
you really want me to add the reserved parameter, in which case I'll release a


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