* One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx> [140707 06:22]: > On Fri, 4 Jul 2014 18:34:10 +0200 > Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > > While comparing the OMAP-serial and the 8250 part of this I noticed that > > the the latter does not use runtime-pm. > > Yes it does, but 8250 parts (generally - omap presumably is special > here ?) need to be powered on to transmit/receive not just for register > access. The core uart layer implements a "pm" operation for this. At least for omaps the UARTs need to be idled for the SoC to hit off-idle where the SoC is powered off and rebooted during idle. So we can certainly enable this in a generic way, however, this can only be done under the following conditions: 1. We can save and restore the serial register context and detect when context was lost in the serial driver. The context loss can be detected by looking at some registers that are only initialized during init. 2. There's a way for the serial RX pin to wake the SoC. On some omaps there's a separate pin specific wake-up interrupt that can be used for that. 3. The serial PM features must be only enabled if requested by the user via sysfs. Typically extra latency and loss of the first RX character occur which is not acceptable to most applications. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
