Re: [PATCH] serial: imx: add rx and tx led trigger

[Arnd Bergmann <arnd@arndb.de>]

On Thursday, July 7, 2016 10:33:22 AM CEST Uwe Kleine-König wrote:
> On Thu, Jul 07, 2016 at 10:27:51AM +0200, Arnd Bergmann wrote:
> > On Thursday, July 7, 2016 8:28:00 AM CEST Uwe Kleine-König wrote:
> > > On Wed, Jul 06, 2016 at 10:09:39PM +0200, Arnd Bergmann wrote:
> > > > On Wednesday, July 6, 2016 7:30:57 PM CEST Uwe Kleine-König wrote:
> > > > > On Wed, Jul 06, 2016 at 05:22:40PM +0200, Arnd Bergmann wrote:
> > > > > > On Monday, July 4, 2016 5:50:09 PM CEST Uwe Kleine-König wrote:
> > > > > > > On Mon, Jul 04, 2016 at 05:43:03PM +0200, Arnd Bergmann wrote:
> > > > > > > > On Monday, July 4, 2016 5:34:12 PM CEST Uwe Kleine-König wrote:
> > > > > > > > > Add support for two led triggers per UART instance that blink on
> > > > > > > > > transmission and reception of data respectively.
> > > > > > > > > 
> > > > > > If this is something we may want to do on other platforms as well,
> > > > > > we should perhaps not hardwire the name of the imx tty device in
> > > > > > the led trigger name.
> > > > > 
> > > > > I cannot follow. If we have several serial lines and a trigger for each
> > > > > of them, they must get different names. Using the device's name to
> > > > > distinguish them seems like a good and obvious idea.
> > > > 
> > > > The main problem I see is if someone puts the name of the trigger into
> > > > a dtb file, as this hardcodes the connection between the Linux driver
> > > > name and numbering system with the device tree binding, which are normally
> > > > separate.
> > > > 
> > > > If we could derive the trigger name from the "/aliases/serial%d" property
> > > > in DT instead, it would get a little more portable.
> > > 
> > > Alternatively we could invent a more dtish way as aliases seem to be
> > > frowned upon [1], something like:
> > > 
> > >     led#0 {
> > >             label = "userled";
> > >             linux,default-trigger = &uart1, "tx";
> > >     };
> > > 
> > >     uart1: serial@43f90000 {
> > >             ...
> > >             #trigger-cells = <1>;
> > >     };
> > 
> > That looks nice, but I don't see how we could implement this in a
> > backwards compatible way, as we don't know whether the first cell
> > of the property is a phandle or a string.
> 
> If we agree, that this is OS-agnostic, we could use "default-trigger" as
> property name instead of "linux,default-trigger".

Yes, I think that can work, but why not just use linux,default-trigger="serial%d-tx"
where serial%d is the alias we already have?

	Arnd