On Mon, 2018-11-12 at 15:36 +0100, Oliver Neukum wrote: > On Mo, 2018-11-12 at 12:04 +0000, Mayuresh Kulkarni wrote: > > > > I think I now understand the disconnect between us this point. Below is an > > attempt to bridge that, so please bear with me: > > 1. In our use-case(s), the end user can "interact" with composite USB device > > either by physically interacting with or via an app on Android. > > 2. When the interaction is "physical" (e.g.: something that is sensed by a > > sensor or a button press), we need "remote-wake" from USB device to host. > > 3. When the interaction is via app (e.g.: to toggle some control), we need > > "host-wake" from host to USB device. > All of these events can occur at the same time. > And you cannot prevent that. > > > > > And this is where, the knowledge of wake-up source and difference in > > handling > > comes into picture. > > For (2), the host needs to first wake-up and then queue a request to read- > > out > > "what" happened. > > For (3), the host needs to first wake-up the device and then queue the > > command(s) to the take action asked by the end user. > > > > I agree that in both of above cases, "a USB request" needs to be send from > > user- > > space to kernel to device. But in my opinion, each of the them has a > > different > > context associated with it. E.g.: for (2), a single read request is > > sufficient > > to "know" what happened while for (3), a write and a read request is needed. > There is a natural race condition between remote and host wake up. > You cannot rule out that your app wakes the device up, exactly when > user interaction would have woken it anyway. > > Your app will know what it wants to do with the device. And you can > detect that. > Hence the correct algorithm is: > > 1. wake up the device > 2. query it for a cause of wake up > 3. If the host wants to do IO, do all of it. > Understood this for remote-wake part. But still unclear about step (1) for host-wake as below (please note, I am refering to host-wake and remote-wake as per my previous comment) - Pre-condition: device in suspend and link in L2. Use-case: end user wants to sends a control message to device. Assumption: end user is NOT doing any activity that causes remote-wake. So how would (1) happen i.e.: which ioctls the user-space should execute? Could you please explain a bit more? > Regards > Oliver
