On Tue, May 23, 2017 at 12:43 AM, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> wrote: > Hi Rob, > >> Am 23.05.2017 um 04:26 schrieb Rob Herring <robh+dt@xxxxxxxxxx>: >> >> On Sun, May 21, 2017 at 5:44 AM, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> wrote: >>> Since our proposed API was not acceptable and the new serdev API has arrived in 4.11 kernels, >>> we finally took the challenge to update the w2sg and w2cbw drivers to use the serdev API. >>> >>> The approach is to write a "man in the middle" driver which is on one side a serdev client >>> which directly controls the UART where the device is connected to and on the other side >>> presents a new tty port so that user-space software can talk to the chips as if they would >>> directly talk to the UART of the SoC (e.g. ttyO1). This is similar to connecting to a remote >>> serial device e.g. through USB (ttyACM) or Bluetooth UART profiles. >>> >>> For example gpsd or hciattach expect a /dev/tty they can control (flow control, baud rate >>> etc.). >> >> I understand from the prior discussion why you want to pass the data >> thru for gps, but why do you need to do that for BT? > > Because we otherwise can't turn on power when /dev/ttyBT0 is opened and turn off when it > is closed. I.e. it should not be powered unless someone does a hciattach /dev/ttyBT0. And it > should be turned off by a killall hciattach. Still, you can do power control within BT HCI drivers. You wouldn't be limited to just open/close, but can handle suspend/resume as well. > Basically we would like to have a power control automatic like it exists for many other devices. > > Since the BT chip is described as a serdev by DT, we see no other means than to pass data > through the serdev driver. We could have a blacklist if we need to have serdev not create a device and create a tty device instead. > We had looked into the line discipline approach but it makes a lot of problems. The first one > is that registering a new system-wide ldesc number is required. Next we do not see how to make > a serdev driver (as it seems to be required by the DT) to register a different ldesc. > >> >>> Here is the result of our first hack which is working as a demo on GTA04 devices (and the >>> w2cbw driver can also be used to control a GTA04 variant with WL1837). >>> >>> Since it is just a demo hack, the code is not yet cleaned up, nor does it completely pass >>> check-patch, nor follows 100% the coding styles. And certainly has some bugs. >>> >>> The most significant issue is that calling tty_port_register_device() inside of the >>> serdev probe() function makes the serdev probe() function to be entered a second >>> time. This does not lead to big problems since we currently have minor = 0 >>> and this makes the second call assume the device is not available. >>> >>> But we have no idea why this happens and how it can be prevented. >> >> Johan's fixes may help there, but it is intended to be temporary to >> have a separate API for registering tty ports with or without serdev. > > Ah, would that mean something like a tty_port_register_device_without_serdev()? Yes, but other way around. The old function doesn't register with serdev and there's a new function that will. > Do you have a reference to his fixes? They are in Greg's tty-linus branch if not Linus' tree now. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
