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

["B48286@xxxxxxxxxxxxx" <B48286@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: geert.uytterhoeven@xxxxxxxxx [mailto:geert.uytterhoeven@xxxxxxxxx]
> On Behalf Of Geert Uytterhoeven
> Sent: Tuesday, March 18, 2014 4:56 PM
> To: Hou Zhiqiang-B48286
> Cc: Mark Brown; linux-spi@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> rob.herring@xxxxxxxxxxx; pawel.moll@xxxxxxx; mark.rutland@xxxxxxx;
> ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx;
> grant.likely@xxxxxxxxxxxx; Wood Scott-B07421; Hu Mingkai-B21284
> Subject: Re: [PATCH 2/2] spi/fsl-lib: Get the SPI controller bus number
> from DTS
> 
> On Tue, Mar 18, 2014 at 8:40 AM, B48286@xxxxxxxxxxxxx
> <B48286@xxxxxxxxxxxxx> wrote:
> >> > > 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.
> >
> > The bus number is the variable designed to distinguish one spi
> > controller from others. Why spi controller's physical address must be
> > use instead of bus number?
> 
> Because the bus number is dynamic, while the physical address doesn't
> change, so it can be used to uniqely identify the device before booting
> the kernel.
> Cfr. "spi1" vs. "e6e20000.spi".
> 

The precondition of dynamic bus number is initial it with -1 in the controller
driver. But now I need a reasonable bus number, I don't want a dynamic one.
Why does use the controller's physical address to take the role of bus number
to distinguish controllers. 

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> In personal conversations with technical people, I call myself a hacker.
> But when I'm talking to journalists I just say "programmer" or something
> like that.
>                                 -- Linus Torvalds
> 

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