[PATCH 2/2] clk: bcm2835: Skip PLLC clocks when deciding on a new clock parent

Martin Sperl kernel at martin.sperl.org
Sat Apr 30 02:28:25 PDT 2016

> On 26.04.2016, at 21:39, Eric Anholt <eric at anholt.net> wrote:
> If the firmware had set up a clock to source from PLLC, go along with
> it.  But if we're looking for a new parent, we don't want to switch it
> to PLLC because the firmware will force PLLC (and thus the AXI bus
> clock) to different frequencies during over-temp/under-voltage,
> without notification to Linux.
> On my system, this moves the Linux-enabled HDMI state machine and DSI1
> escape clock over to plld_per from pllc_per.  EMMC still ends up on
> pllc_per, because the firmware had set it up to use that.
> Signed-off-by: Eric Anholt <eric at anholt.net>
> Fixes: 41691b8862e2 ("clk: bcm2835: Add support for programming the audio domain clocks")
I guess this patch looks to me as if it is a policy inside the kernel,
which is AFAIK frowned upon.

I am looking into making "assigned-clock-parents” inside the dt 
work with the driver.

Could look something like this:
i2s: i2s at 7e203000 {
	assigned-clock-parents = <&cprman BCM2835_PLLD_PER>, <&clk_osc>;
	assigned-clocks = <&cprman BCM2835_CLOCK_PCM>, <&cprman BCM2835_CLOCK_PCM>;
(not sure if that works really - the same clock in assigned-clocks looks suspicious)

This would move the policy out of the kernel into the device-tree,
which - i guess is a better solution.


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