Re: [PATCH 1/3] can: m_can: add Bosch M_CAN controller support

[Dong Aisheng <b29396@freescale.com>]

On Thu, Jul 03, 2014 at 11:04:36AM +0200, Marc Kleine-Budde wrote:
> On 07/03/2014 10:48 AM, Dong Aisheng wrote:
> > On Thu, Jul 03, 2014 at 09:12:49AM +0200, Marc Kleine-Budde wrote:
> >> On 07/03/2014 05:48 AM, Dong Aisheng wrote:
> >>> On Wed, Jul 02, 2014 at 09:13:07PM +0200, Marc Kleine-Budde wrote:
> >>>> On 07/02/2014 07:54 PM, Oliver Hartkopp wrote:
> >>>>> I'm not really familiar with the naming concept in device trees.
> >>>>>
> >>>>> What is your opinion about the remarks below?
> >>>>
> >>>> The entries in the DT, at least on freescale baords, follow the naming
> >>>> scheme of the reference manual. E.g. on the mx25 it's can1 and can2:
> >>>>
> >>>>     can1: can@43f88000 { ... }
> >>>>     can2: can@43f8c000 { ... }
> >>>>
> >>>> And on the mx28, its:
> >>>>
> >>>>     can0: can@80032000 { ... }
> >>>>     can1: can@80034000 { ... }
> >>>>
> >>>> Because the imx25 datasheet uses a "1" based counting scheme, while the
> >>>> imx28 uses a "0" based one.
> >>>>
> >>>> So it's best practise to follow the naming and numbering scheme of the
> >>>> hardware reference manual.....and if you have access to the
> >>>> documentation of the m_can core, use clock names of the m_can core for
> >>>> the clock-names property.
> >>>>
> >>>
> >>> Based on my knowledge, device tree allows define phandle name according to
> >>> the real device name of HW according spec while the device node name should
> >>> be general(e.g can@80032000 rather than flexcan@80032000).
> >>> For imx6sx, there are already following entries in
> >>> arch/arm/boot/dts/imx6sx.dtsi
> >>> flexcan1: can@02090000 {...}
> >>> flexcan2: can@02094000 {...}
> >>> So i'd prefer to define as:
> >>> m_can1: canfd@020e8000 {...}
> >>> m_can2: canfd@020f0000 {...}
> >>>
> >>>
> >>> One problem is there're can alias already.
> >>> aliases {
> >>> 	can0 = &flexcan1;
> >>> 	can1 = &flexcan2;
> >>> 	...
> >>> }
> >>> I'm not sure adding can2&can3 for mcan is properly:
> >>> aliases {
> >>> 	can0 = &flexcan1;
> >>> 	can1 = &flexcan2;
> >>> 	can2 = &m_can1;
> >>> 	can3 = &m_can2;
> >>> 	...
> >>> }
> >>> Since the m_can driver does not need to use aliases,
> >>> so i will not add them.
> >>
> >> IMHO It's fine too add the can{2,3} aliases to m_can, too.
> >>
> > 
> > I think the main problem for doing this way is that the meaning of id
> > return by of_alias_get_id may be not persistent.
> > e.g
> > For MX6SX
> > aliases {
> > 	can0 = &flexcan1;
> > 	can1 = &flexcan2;
> > 	can2 = &m_can1;
> > 	can3 = &m_can2;
> > 	...
> > }
> > 
> > For other platform, it could be:
> > aliases {
> > 	can0 = &m_can1;
> > 	can1 = &m_can2;
> > 	...
> > }
> > It's hard for driver to use.
> 
> The driver doesn't make use of it, does it?
> 
> > And actually the M_CAN driver does not need to use the alias.
> > So i wonder if it makes sense to add the alias for m_can devices
> > like that.
> 
> For example the imx53 has two different SPI units, in the alias section
> we see:
> 
>                 spi0 = &ecspi1;
>                 spi1 = &ecspi2;
>                 spi2 = &cspi;

Thanks for the info.
I'm not clear what's our purpose adding alias like this?
Can you help explain it a bit?
Do we need adding alias for all exist devices?

Regards
Dong Aisheng

> 
> Marc
> 
> -- 
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |
>