From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] serial: imx: add rx and tx led trigger Date: Thu, 07 Jul 2016 10:27:51 +0200 Message-ID: <6724841.mKIqTiexKe@wuerfel> References: <1467646452-21243-1-git-send-email-u.kleine-koenig@pengutronix.de> <3835401.kFNahHioV5@wuerfel> <20160707062800.GT16643@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20160707062800.GT16643@pengutronix.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: linux-arm-kernel@lists.infradead.org Cc: kernel@pengutronix.de, linux-serial@vger.kernel.org, Uwe =?ISO-8859-1?Q?Kleine=2DK=F6nig?= List-Id: linux-serial@vger.kernel.org On Thursday, July 7, 2016 8:28:00 AM CEST Uwe Kleine-K=F6nig wrote: > Hello Arnd, > = > [adding Rob Herring to Cc] > = > 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-K=F6nig 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-K=F6nig 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-K=F6nig wrot= e: > > > > > > > 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 ea= ch > > > 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 norma= lly > > separate. > > = > > If we could derive the trigger name from the "/aliases/serial%d" proper= ty > > 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 =3D "userled"; > linux,default-trigger =3D &uart1, "tx"; > }; > = > uart1: serial@43f90000 { > ... > #trigger-cells =3D <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. > Having said that, I don't think it's a big problem if the value of > "linux,default-trigger" is Linux-specific. Moreover, is a default > trigger considered a hardware description? What's more important here I think is that even in Linux, the name of the uart is not always stable across versions or configurations, e.g. in on OMAP we can have either ttyO%d or ttyS%d. Arnd