[PATCH] pl011: added clock management feature

[Grzegorz.Sygieda at tieto.com]

>On Tue, Nov 09, 2010 at 02:40:12PM -0800, Greg KH wrote:
>> On Tue, Nov 09, 2010 at 04:30:37PM +0100, Linus Walleij wrote:
>> > From: Grzegorz Sygieda <grzegorz.sygieda at tieto.com>
>> > 
>> > This patch allows to control the pl011 clock using set_termios 
>> > callback. Any positive baudrate passed enables clock, otherwise 
>> > disables. This saves a lot of power on submicron designs since we 
>> > can clock off and disable unused UARTs.
>> 
>> That's nice, but it seems like an overload of what people 
>> traditionally think of when it comes to baud rates.  Why not just 
>> power down ports that are not open instead?
>
>We already do.  My question to Linus (in a previous message) is why this isn't sufficient.

The main goal was to disable/enable clock while port open. This is usefull for scenario, where some higher level driver wants to control the power consumption (using set_termios). In the same time a user-space app (eg. hciattach) is still bounded to the specific /dev/tty* device associated with particular uart. From user POV device is always open, and app does not have to respawn, and we can save power.

I hope it's clear explanation.