linux-kernel - Re: [RFCv1 5/5] arm64/ARM: configs: Change CONFIG_PWM

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Date:   Fri, 18 Oct 2019 20:10:43 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Anand Moon <linux.amoon@...il.com>
Cc:     Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic@...ts.infradead.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv1 5/5] arm64/ARM: configs: Change CONFIG_PWM_MESON from m to y

Hi Anand,

On Fri, Oct 18, 2019 at 4:04 PM Anand Moon <linux.amoon@...il.com> wrote:
[...]
> > Next step it to try narrow down the clock causing the issue.
> > Remove clk_ignore_unused from the command line and add CLK_INGORE_UNUSED
> > to the flag of some clocks your clock controller (g12a I think) until
> >
> > The peripheral clock gates already have this flag (something we should
> > fix someday) so don't bother looking there.
> >
> > Most likely the source of the pwm is getting disabled between the
> > late_init call and the probe of the PWM module. Since the pwm is already
> > active (w/o a driver), gating the clock source shuts dowm the power to
> > the cores.
> >
> > Looking a the possible inputs in pwm driver, I'd bet on fdiv4.
> >
>
> I had give this above steps a try but with little success.
> I am still looking into this much close.
it's not clear to me if you have only tested with the PWM and/or
FCLK_DIV4 clocks. can you please describe what you have tested so far?

for reference - my way of debugging this in the past was:
1. add some printks to clk_disable_unused_subtree (right after the
clk_core_is_enabled check) to see which clocks are being disabled
2. add CLK_IGNORE_UNUSED or CLK_IS_CRITICAL to the clocks which are
being disabled based on the information from step #1
3. (at some point I had a working kernel with lots of clocks with
CLK_IGNORE_UNUSED/CLK_IS_CRITICAL)
4. start dropping the CLK_IGNORE_UNUSED/CLK_IS_CRITICAL flags again
until you have traced it down to the clocks that are the actual issue
(so far I always had only one clock which caused issues, but it may be
multiple)
5. investigate (and/or ask on the mailing list, Amlogic developers are
reading the mails here as well) for the few clocks from step #4

> Well I am not the expert in clk or bus configuration.
> but after looking into the datasheet of for clk configuration
> I found some bus are not configured correctly.
did you find any reason which indicates that the problem is related to a bus?
the issues I had were due to clocks not being assigned to their
consumers in .dts - that can be anything (from a bus to something
different).


Martin