Re: [PATCH] pl011: added clock management feature

[Greg KH <gregkh@suse.de>]

On Wed, Nov 10, 2010 at 10:15:53AM +0200, Grzegorz.Sygieda@tieto.com wrote:
> >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@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.

That is nice, but again, you are overloading a common interface (one
defined by POSIX I think) to do something else at the same time.  That
might cause problems with some users that expect you to be able to use a
baud rate of 0 :)

I like the idea, but not the overloading, sorry.

thanks,

greg k-h