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From: Grant Likely <grant.likely@secretlab.ca>
Date: Tue, 27 Jul 2010 11:43:29 -0600
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Subject: Re: [PATCH v3 2/2] powerpc/mpc5121: add initial support for PDM360NG
	board
To: Anatolij Gustschin <agust@denx.de>
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On Tue, Jul 27, 2010 at 11:28 AM, Anatolij Gustschin <agust@denx.de> wrote:
> On Tue, 27 Jul 2010 10:58:33 -0600
> Grant Likely <grant.likely@secretlab.ca> wrote:
> ...
>> >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 spi@11900 {
>> >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 compatible =3D "fsl,m=
pc5121-psc-spi", "fsl,mpc5121-psc";
>> >> > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 cell-index =3D <9>;
>> >>
>> >> Try to drop the cell-index properties. =A0They are almost always misu=
sed.
>> >
>> > Removing cell-index would require changing the spi driver's probe.
>> > Currently cell-index is used to set spi bus number. What could be used
>> > for bus enumeration instead? Is it okay to use part of the spi node
>> > address? e.g. obtaining the offset 0x11900, masking out the unrelated
>> > bits and shifting by 8 would deliver unique index 9 for PSC9 in SPI
>> > mode. This would work for all 12 PSC SPI controllers of mpc5121.
>>
>> Does the spi bus number really matter? =A0The device tree context gives
>> you a firm association between spi masters and devices which doesn't
>> require assigning a specific bus number. =A0The core spi code can
>> dynamically assign a bus number for the bus by setting bus_num to -1.
>
> The bus number is used in the mpc5121 psc spi driver to obtain correct
> clock for PSC in question (0 to 11) and to enable the PSC clock at probe
> time. Therefore using dynamically assigned bus number would require anoth=
er
> change to the spi driver.

That's unrelated to the bus number.  Use cell-index value directly for
obtaining the clock if you need to; but limit its exposure.  Once
Jeremy gets his common clock architecture merged, then we could
probably migrate to that for obtaining the correct clock without
cell-index.

g.