Em 28-06-2011 03:22, Hans Verkuil escreveu: > On Monday, June 27, 2011 23:20:07 Mauro Carvalho Chehab wrote: >> Em 07-06-2011 12:05, Hans Verkuil escreveu: >>> From: Hans Verkuil <hans.verkuil@xxxxxxxxx> >>> >>> When an application changes a control you want to generate an event. >>> However, you want to avoid sending such an event back to the application >>> (file handle) that caused the change. >> >> Why? >> >> I can see two usecases for an event-triggered control change: >> 1) when two applications are used, and one changed a value that could >> affect the other; >> 2) as a way to implement async changes. >> >> However, it seems, from your comments, that you're covering only case (1). >> >> There are several reasons why we need to support case (2): >> >> Some controls may be associated to a servo mechanism (like zoom, optical >> focus, etc), or may require some time to happen (like charging a flash device). >> So, it makes sense to have events back to the application that caused the change. >> >> Kernel should not assume that the application that requested a change on a control >> doesn't want to receive the notification back when the event actually happened. >> This way, both cases will be covered. >> >> Yet, I failed to see where, in the code, such restriction were imposed. > > Async changes are triggered by the driver, not an application. Any changes > made by the driver will be sent to all applications. > > That said, I think I should add a flag like V4L2_EVENT_SUB_FL_NO_FEEDBACK > to explicitly let applications decide. Agreed. it makes the code more generic. > > That's easy enough. > > Regards, > > Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
