PATCH[1/1] 8xx: Add clock-frequency to .dts brg entries

Scott Wood scottwood at
Wed Jan 30 03:26:11 EST 2008

On Mon, Jan 28, 2008 at 11:55:20PM +0000, Bryan O'Donoghue wrote:
> You mean that arch/powerpc/boot/mpc8xx.c mpc8xx_set_clocks is supposed
> to be adding this field ? 

Yes.  Or u-boot, if you're not using the bootwrapper/cuImage.

> I see arch/powerpc/boot/wrapper.a has a reference to the function but -
> and this time I've checked all documentation - there's no mention of how
> to use this library at all... it _looks_ to me like this isn't being
> linked in any way.
> It for sure is nowhere in the uImage - and I've taken the preferred
> route of making a uImage with .dtb - genreated from adder875-uboot.dts

In that case, u-boot needs to add that property.

> dtc -O -o adder875-uboot.dtb arch/powerpc/boot/dts/adder875-uboot.dtb

You'll want to use the -p option to add some extra space for u-boot to

> cpm_uart depends on "fsl,cpm-brg" and a field called "clock-frequency"
> as I understand it that's
> fsl,cpm-brg
> 	|_clock-frequency
> whereas mpc8xx_set_clocks seems to add
> /soc/cpm/brg
> 	|_clock-frequency

The fsl,cpm-brg refers to the compatible property, not the node name.

> mpc866ads.dts - also has a "fsl,cpm-brg" => clock-frequency entry in 
> linux/arch/powerpc/boot/dts/mpc866ads.dts - and to me this looks like
> the correct approach for get_brgfreq to function properly...

And it's zero, meaning that you still need u-boot or the bootwrapper to
fill in the correct value.  The only difference is whether there's a
placeholder property -- they used to be required by older u-boots, but
are no longer necessary.


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