Re: [PATCH v3 2/2] powerpc/mpc5121: add initial support for PDM360NG board

On Tue, Jul 27, 2010 at 11:28 AM, Anatolij Gustschin [off-list ref] wrote:

On Tue, 27 Jul 2010 10:58:33 -0600
Grant Likely [off-list ref] wrote:
...

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+ =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";

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+ =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.

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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.