Hi, On 12/07/2010 09:01 PM, Mauro Carvalho Chehab wrote:
Hi Jean-Fronçois, git commit 35680baa6822df98a6ed602e2380aa0a04e18b07 (see enclosed) caused not only a regression at PS/3 Eye webcam (git commit f43402fa55bf5e7e190c176343015122f694857c), but also at sn9c201 driver, when used on SXGA mode. What happens is that only the highest alternate mode is enough for the maximum resolution. I suspect that other drivers broke due to that change. So, IMO, the better is to revert and work on another alternative.
I have to agree with Mauro here, dropping back to a lower alt setting for all devices with a usb audio interface is the wrong thing to do. For example I know multiple devices where the highest alt setting does not have a wMaxPacketSize of 1023, but use something lower instead, to make sure there is enough bandwidth left for usb audio even if the highest alt setting get used.
Btw, no matter what resolution is used, sn9c201 is setting the same alternate for all modes, spending more USB bandwidth than needed. Why gspca is just getting the highest value for wMaxPacketSize? It should, instead, seek for the minimum packet size that is needed for a given resolution.
There are 2 reasons for this: 1) We do not know the minimum packetsize for a given resolution, unlike with uvc where this is arranged in the protocol, for proprietary apps we can only guess 2) Almost all devices supported by gspca are usb-1.1 and thus the framerate is bandwidth limited. We want to deliver the highest framerate possible, and thus get as high an alt setting as possible. I most note that many gspca subdrivers are defective wrt how this is all handled though, in that they don't vary the framerate when the available bandwidth changes. So in many cases if the gspca core cannot get the highest alt setting things may not function at all (because the subdriver fails to select a lower framerate, resulting in parts of frames getting dropped due to bandwidth limitations). Fixing this requires: 1) Figuring out how to change the framerate for each sensor + bridge combo 2) Testing to see what framerate will still work at which alt setting 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
