On Fri, Apr 25, 2014 at 11:34 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Thu, 24 Apr 2014 15:19:14 +0100 One Thousand Gnomes > <gnomes@xxxxxxxxxxxxxxxxxxx> wrote: > >> > > But I don't have discrete hardware. I have a bunch of stuff soldered onto a >> > > board with ad-hoc connections chosen to make the life of the hardware builder >> > > easy rather than chosen to make the life of the software developer easy >> > > (which I think is the correct choice). >> > > >> > > So I need to tell DT "This device is plugged into this UART, and there is no >> > > DTR line, but when the UARTs DTR line would be asserted (if it had one), then >> > > I need that regulator of there turned on". or maybe "I need to toggle this >> > > GPIO with exactly this pattern, while watching that GPIO to see if it is >> > > working". >> > > >> > > So I thought: >> > > >> > > 1/ give the UART a "virtual" DTR so it could drive any GPIO >> > > 2/ create a "gpio-to-regulator" driver which presented as a (virtual) gpio >> > > and responded to state changes on that GPIO by turning on or off the >> > > regulator >> > > 3/ create a dedicated driver which knows how to toggle the magic GPIO while >> > > watching the other GPIO to convince the silly device to wakeup, or go to >> > > sleep, as required, and have this appear as a (virtual) GPIO. >> >> Unless you are using it as a "real' DTR line then I think this is the >> wrong approach. This problem actually is turning up in both PC class and >> ARM boxes now all over the place for three reasons I am seeing. >> >> 1. We are getting a lot of hardware moving to serial attached >> bluetooth/gps/etc because of the power win. In addition ACPI can describe >> power relationships and what is on the other end of a UART embedded in >> the device >> >> 2. We've got cheap hardware with modem lines being "retrofitted" via gpio >> >> 3. There are a subset of devices that have extra control lines beyond the >> usual serial port ones. These range from additional control lines for >> things like smartcard programmers to port muxing. >> >> > I have no problem either way, just that unused code doesn't have to be >> > sitting in the tree and I'm not entirely sure this GPIO should be >> > handled by omap-serial.c, perhaps something more generic inside >> > serial-core so other UART drivers can benefit from it. >> >> serial-core provides power hooks. If the goal is that this comes on when >> you power up the uart and goes away on the last close then the hooks are >> there already. > > Could you be a bit more explicit, or point to an example user of these hooks? > > I had a quick look and I guess that uart_change_pm() is the most likely > candidate for what you are referring to. > I can see how that interfaces to the specific piece of uart hardware, such as > omap-serial.c > But I cannot see how you would plumb that though to the device that was > plugged in to the serial port. I guess if that device could be registered as > a child of the omap_serial device, then power management inheritance might > come in to play, but I cannot see any way to tell a serial port that it has > some arbitrary child device. > > So maybe I'm missing something. > >> If its ldisc specific then the tty layer also calls the >> device on ldisc changes precisely so it can make hardware specific >> twiddles in such cases. >> >> A set of gpios on the tty_port object would not go amiss and would also >> address the PC case. >> >> > considering this is a BTUART device, why didn't you do this at the ldisc >> > level ? hci_uart_open() sounds like a good choice from a quick thinking. >> >> ldiscs are hardware independent. Nothing about hardware belongs in an >> ldisc. Any ldisc should within reason work on any port. >> >> What I propsed when it came up ages ago was to expose some gpio settings >> in the tty, to provide ways for them to be set by default and also ioctls >> to configure them. I still think this (but moved into the tty_port as its >> a persistent hardware property) is a good idea now that we are starting >> to see more use cases than weird dongles and muxes on pre-production >> reference boards. >> >> With my tty and serial hat on I think a power gpio is a no-brainer even >> without doing the other work and therefore it should probably be described >> generically for a serial port in the DT as well as in the ACPI data. If >> you should also be able to give it a regulator to use as well that also >> seems to make complete sense. > > In one case the "power on" sequence is substantially more complex that just a > gpio or regulator. I would need to write a device driver for the (GPS) chip > which could receive a poweron/poweroff signal from the uart and do the > required magic. > > Having serial-core know about gpios and regulators and random other stuff > seems wrong. > I would really like to see the "runtime interpreted power sequences" become a > real thing. Then serial-core could activate a "RIPS", and that would have > the flexibility to do whatever is needed without adding complexity to > serial-core. > Using a virtual GPIO was my poor-mans RIPS. Using gpiolib, and driver can > pretend to be a gpio so it is a simple "pipe" to send a power-on/power-off > signal over. > > So ... with your "serial" hat on, if I were to write/test a patch to allow > any serial port to have a "power-gpio" described in DT and the gpio would be > driven in uart_change_pm(), would you consider accepting that patch, or did I > misunderstand? As soon as this patch (http://www.spinics.net/lists/arm-kernel/msg325197.html) will be applied, we don't really need this DTR GPIO any more. DTR_active is the only stuff, that is missing. Yegor -- 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
