Oliver Neukum <oneukum@xxxxxxxx> writes: > On Fri, 2016-05-13 at 18:59 +0200, Bjørn Mork wrote: >> Bjørn Mork <bjorn@xxxxxxx> writes: >> >> > The driver enforces a strict one-to-one relationship between the >> > received RESPONSE_AVAILABLE notifications and messages read from >> > the device. At the same time, it will cancel the interrupt URB >> > when there is no client holding the character device open. >> >> Never mind. Forget it. >> >> This patch breaks other devices again. The immediate and unconditional >> reading make them barf. I guess it can be worked around by delaying the >> flushing until at least one notification is received, but I obviously >> have to test this theory thoroughly on all devices I have. > > Hi, > > I think the best approach would be to keep the interrupt URB always > active. I didn't do this to conserve bandwidth, but if it makes devices > work, it certainly would be the best option. Yes, I considered that. But this implies purging the device message queue without telling userspace that we did so. At least with the current driver design, which is based on a single limited size buffer. If the device queues a number of unsolictied messages between two userspace requests, then we really want all those unsolicted messages delivered to the userspace program on the second request. And I do think the original bandwidth (and power) conservative approach is worth keeping too. There is no point in waking up these devices unless there actually is an interested userspace application. FWIW, my initial analysis of the problem with the patch was too quick imprecise. The problem is simply the -EPIPE status we inevitably will hit when the queue is empty, as I should have anticipated. It will be returned to userspace translated to -EIO. I am currently testing a version taking care of that, and it seems to behave well so far. I'll submit it as soon as I am absoltely sure that it works on all WDM, QMI and MBIM devices I have. Might take some time, since I am running out of mini-PCIe and m.2 adapters.. Bjørn -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
