Messages in this thread | | | Subject | Re: [PATCH 2/2] clk: bcm2835: Skip PLLC clocks when deciding on a new clock parent | From | Martin Sperl <> | Date | Mon, 2 May 2016 18:36:24 +0200 |
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> On 02.05.2016, at 17:29, Eric Anholt <eric@anholt.net> wrote: > > Martin Sperl <kernel@martin.sperl.org> writes: > >>> On 26.04.2016, at 21:39, Eric Anholt <eric@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@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. > > Can you come up with a use for putting peripherals on PLLC ever, such > that we need choice?
For PLLC not right now, but with clk_notifier_register drivers could work around those clock changes (assuming we get that information from the firmware somehow - or if we could move this decision into the kernel: even better).
But I can come up with a scenario that would make use of the pllh_aux under some circumstances - e.g when requesting 290039Hz on clock gp0/1/2.
Similarly: if we ever enable the testdebugX clocks these become immediate candidates for parent-clocks as well which can result in more headache.
Being able to define which clocks to use at least give the dts author a means also to control clock selection if he wants to enable the testdebug clocks.
Another similar situation can occur with plla_per - under some circumstances it may get used unexpectedly.
Martin
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