Hi,
On 09/13/2013 02:35 PM, Nathan Hjelm wrote:
>
> On Sep 13, 2013, at 3:18 AM, Hans de Goede <[email protected]> wrote:
<snip>
>> 2) The alloc_streams backend op should not fail when the user requests more
>> streams
>> then available, instead it should simply allocate the number of
>> available streams
>> available and return that (as mentioned in the doxygen docs)
>>
>> So this is wrong:
>>
>> + (*(cInterface->interface))->SupportsStreams (cInterface->interface,
>> pipeRef, &supportsStreams);
>> + if (num_streams > supportsStreams) {
>> + rc = LIBUSB_ERROR_INVALID_PARAM;
>> + break;
>> + }
>>
>> And should be:
>>
>> + (*(cInterface->interface))->SupportsStreams (cInterface->interface,
>> pipeRef, &supportsStreams);
>> + if (num_streams > supportsStreams)
>> + num_streams = supportsStreams
>>
>> Note the check for how many streams are supported is done inside the kernel
>> with Linux, and it will continue with the maximum number of streams supported
>> if the user request more streams, so it is hard to implement any other logic
>> under Linux, while it seems easy to mimick the Linux behavior with darwin.
>
> Hmm, what exactly are the semantics under Linux if the endpoints support a
> different number of streams?
The xhci driver (which implements this) first iterates over all endpoints to
find the minimum support by
all of them. Then if the minimum <= 1 it bails with an error (no streams
supported on 1 or more eps), if
the minimum > 1, it allocates the minimum found on all eps.
> To mimic I will either need to take the minimum first and allocate that for
> each endpoint (returning an error if any endpoint returns 0 supported
> streams) or just allocate the smaller of num_streams or the maximum supported
> streams for each endpoint and return the mimimum.
Right, you need to "calculate" the minimum first.
>
>> Maybe we should log a warning when returning less streams then requested?
>> If we want to log a warning it would be best to actually do that in the
>> core.c alloc_streams wrapper, so that it is consistently done for all
>> backends.
>
> Sounds fine to me.
Regards,
Hans
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