On 07/09/2014 01:17 PM, Tony Lindgren wrote: > * 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. A register check on restore context? DLL+DLH might be a good hint here since its value should be >0 in the running case. > > 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. That one would be handled by omap separately. > 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. Unless I'm mistaken the omap driver now initializes the timeout to -1. So nothing happens unless this is enabled separately. > Regards, > > Tony > Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
