Re: [PATCH 2/2] spi/fsl-lib: Get the SPI controller bus number from DTS

[Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Mon, Mar 17, 2014 at 05:11:11AM +0000, B48286-KZfg59tc24xl57MIdRCFDg@public.gmane.org wrote:
> > On Fri, Mar 14, 2014 at 05:35:57PM +0800, Hou Zhiqiang wrote:
> > > Get the spi_master's bus_num from DTS to make the spi_master's name
> > > static. So "mtdparts=spi.bus_num.chip_select:..." in cmdline can be
> > > used to asign mtd partions of spi flash.

> > If we are going to do this it shouldn't be device specific (it should be
> > done in the framework since nothing is specific to the controller there)
> > but I'm not convinced that we should be doing it - this is all very Linux
> > specific.

> This patch just assign a bus number to the controller. It is driver's 
> responsibility to distribute a bus number to spi_master and the definition
> of bus_num is used to distinguish controllers. So, it is specific for the
> controller and doesn't affect the framework. 

You are adding a property to specify a bus number.  There is no reason
why such a property should be specific to a single controller, every
controller in every system has a bus number assigned to it so if we have
a way to specify one controller via the device tree we should have a way
to specify it for all.

> > The DT already has support for specifying flash layouts, can't those be
> > used (for example via chosen if they're not fixed for the board)?  Or if
> > it's just picking the correct filesystem then UUIDs and labels are the
> > standard way to do things.

> The DT specifying flash layouts is ok. There is another way to make the
> flash layouts using command line, but it is not safe because of the dynamic
> bus_num. It is not the reason that the way of DT is supported flash layouts,
> to live the other way unsafe, right?

This sounds to me like we need a better way of talking about flash
device names on the Linux command line rather than a way to fix the bus
number - for example, being able to refer to them using a fixed property
like the physical address.  Being able to refer to devices via an alias
assigned in the DT would also be useful (and more readable), I think
there may already be a mechanism for doing that which would need to be
plumbed in but I'm not 100% sure.

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