Martin Sperl [off-list ref] writes:

Sent from my iPad

quoted

On 26.04.2016, at 21:31, Eric Anholt [off-list ref] wrote:

kernel at martin.sperl.org writes:

quoted

From: Martin Sperl <redacted>

The bcm2835 firmware enables several clocks and plls before
booting the linux kernel.

These plls should never get disabled as it may result in a
stopped system clock and more.

So during probing we check if the pll_divider is enabled
and if it is then mark that pll_divider as critical.
As a consequence this will also enable the corresponding parent pll.

Here the list of pll_div that are marked as critical:
[    2.022437] bcm2835-clk 20101000.cprman: found enabled pll_div plla_core - marking it as critical
[    2.031640] bcm2835-clk 20101000.cprman: found enabled pll_div pllb_arm - marking it as critical
[    2.040966] bcm2835-clk 20101000.cprman: found enabled pll_div pllc_core0 - marking it as critical
[    2.050351] bcm2835-clk 20101000.cprman: found enabled pll_div pllc_per - marking it as critical
[    2.059427] bcm2835-clk 20101000.cprman: found enabled pll_div plld_core - marking it as critical
[    2.068590] bcm2835-clk 20101000.cprman: found enabled pll_div plld_per - marking it as critical
[    2.077724] bcm2835-clk 20101000.cprman: found enabled pll_div pllh_pix - marking it as critical

Yeah, pllh_pix isn't critical, though.  We want it to get turned off
when the driver asks to disable its clock, or we're going to just waste
a pile of power.

I'm sending out a patch that marks the VPU clock as critical (it's the
also AXI bus, so it certainly is critical), which should solve your
aux_uart clock disabling problem, I think.

The problem is that it also fails on the pcm clock alone when pllc or 
plld_per are used as parent, but it is fine when osc is used... 

For that you're going to want the HAND_OFF patches that mturquette is
working on: Don't let the clock and its parents get turned off until a
driver has shown up that has referenced the clock and done at least a
prepare on it once.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 818 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20160426/f949ce9c/attachment.sig>