[PATCH V4 0/7] clk: bcm2835: add clocks and add MASH support

Martin Sperl kernel at martin.sperl.org
Sat Jan 16 01:40:34 PST 2016

> On 15.01.2016, at 15:20, kernel at martin.sperl.org wrote:
> From: Martin Sperl <kernel at martin.sperl.org>
> The clk-bcm2835 driver right now relies on BCM2835_CLOCK_COUNT defined
> in include/dt-binding/clocks/bcm2835.h
> With every new clock introduced this value needs to increase,
> which is not what should happen for bindings.
> So we reorganize the driver so that it is no longer necessary
> to define BCM2835_CLOCK_COUNT.
> Also the driver calculates fractional clock dividers correctly,
> but it does not enable the bit to enable support in the register.
> As a minimal extension we now can also define higher order MASH
> support when defining the clocks.
> There is also an issue when the clock divider is < 2 - in that
> case no clock-output is generate. The clamping code has been
> enhanced to handle this as well.
> Similarly there is also the clamping of the highest divider now
> limited to the highest possible integer divider instead of the
> highest possible fractional diviver.
> Finally we add all the 23 different HW clocks that have not been
> configured in the driver.
> Changelog:
> 	V1 -> V2: split the asoc/sound patches from the clock patches
> 	      	  enable frac/mash support
> 	V2 -> V3: clamp clock divider to be >= 2
> 		  clamp max clock divider to be integer (not fractional)
> 		  added additional limit checks for divider selection
> 		    allowing fallback to lower mash levels.
> 		  use a newer probing mechanism based on a single array
> 	V3 -> V4: fixed bad NULL pointer check in init
> 	      	  fixed (mash) limit checks
> 		  separated basic mash support from limits checks
> 		  really tested with I2S device (unfortunately V3 was
> 		  not well tested in this respect)
> Martin Sperl (7):
>  clk: bcm2835: the minimum clock divider is 2
>  clk: bcm2835: clamp clock divider to highest integer only
>  clk: bcm2835: remove use of BCM2835_CLOCK_COUNT in driver
>  clk: bcm2835: enable management of PCM clock
Please note that Mark Brown has already merged the patch to
bcm2835-i2s that makes use of the PCM-clock added with this patch.

>  clk: bcm2835: add missing 22 HW-clocks.
>  clk: bcm2835: enable fractional and mash support
>  clk: bcm2835: apply limits on dividers to MASH mode.
> drivers/clk/bcm/clk-bcm2835.c       |  583 ++++++++++++++++++++++++++++++-----
> include/dt-bindings/clock/bcm2835.h |   25 +-
> 2 files changed, 521 insertions(+), 87 deletions(-)
> --

There is still some discussion around the best clock selection
method (especially low jitter for PCM and possibly PWM), but as I guess
not all “use-cases” for clocks are identical it would require some

As such parameters typically would go into device-tree here a
proposal for how we could implement the device-tree options:

	clocks: cprman at 7e101000 {
		compatible = "brcm,bcm2835-cprman";
		#clock-cells = <1>;
		reg = <0x7e101000 0x2000>;

		/* CPRMAN derives everything from the platform's
		 * oscillator.
		clocks = <&clk_osc>;

		/* non default override for some clocks */
		clock at BCM2835_CLOCK_PCM {
			reg = <BCM2835_CLOCK_PCM>;

			/* all of the below properties are optional */

			/* only use the following as parents - but must
			 * be a member of all the permissible plls for this
			 * clock.
			 * note that PLLC is used for overclocking
			 * the ARM by downstream kernels, so it should not
			 * get used for PCM.
			parent-clock-names = “xosc”,
			/* alternate clock/divider selector */
			bcrm,clock-selector = <BCM2835_CLOCK_SELECTOR_LOWJITTER>;
			/* minimum divider used for fractional support */
			bcrm,min-div-f = <20>;
			/* alternatively defined explicitly as jitter */
			max-jitter-ns = <500>;
			/* mash_support defining the max MASH order */
			bcrm,max-mash-order = <BCM2835_MASH_ORDER_3>;
			/* possibly other parameters needed by the chosen
			 * clock selector.

Would something like this be acceptable?

I would then create a separate patchset based on this patchset to
introduce those features when I get back.


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