Re: [PATCH] dummy_hcd: add isoc support

[Michael Grzeschik <mgr@pengutronix.de>]

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On Wed, Jan 26, 2022 at 11:09:23AM -0500, Alan Stern wrote:
>On Wed, Jan 26, 2022 at 02:22:49PM +0100, Michael Grzeschik wrote:
>> With this patch, the dummy_hcd gains first support for isoc transfers.
>> It will complete the whole urb with all packages.
>
>"packets", not "packages".

Right.

>>  Even if the gadget
>> side did not enqueue any request, the urb will be handled.
>>
>> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>
>I don't like this idea.  If support for isochronous transfers is added,
>it should be done correctly.  That is, the implementation should support
>scheduling of transfers, periodic bandwidth reservation, high-bandwidth
>transfers, and so on.
>
>The whole point of dummy-hcd is to emulate a real host controller as
>closely as possible.  Real isochronous transfers do not complete all at
>once.

I agree, that whole isoc support needs proper improvement.

I could/should have added RFC to the patch. As the whole intention of
this code, for now, is to validate the gadget/uvc configfs patchseries
mentioned in the the comments.

With this patch, it is at least possible to get the gadget running on
dummy_hcd and try out the "non-isoc dependent" parts, that are actually
changed, in the mentioned series.

The validation of the payload path, actually using the mentioned isoc
endpoints, is left to the developer who implements the missing parts
you mentioned above.

Michael

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