linux-kernel - Re: [PATCH v4] clk: expand clk_ignore_unused mechanism to keep only a few clks on

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Date:   Thu, 30 Mar 2023 19:33:19 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>
Cc:     Jonathan Corbet <corbet@....net>, Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de, linux-clk@...r.kernel.org
Subject: Re: [PATCH v4] clk: expand clk_ignore_unused mechanism to keep only
 a few clks on

Hello Sebastian,

On Thu, Mar 30, 2023 at 05:26:17PM +0200, Sebastian Reichel wrote:
> > > In that case it sounds like you want to compile the kernel with the
> > > support for enabling clks from debugfs. Can you use that?
> > 
> > In some of the cases that might work. Unless for example the problem
> > makes the kernel fail to boot or the device is broken when the clk was
> > disabled and reenable doesn't help?!
> 
> I recently debugged a similar issue like this:
> 
> 1. build kernel with CLOCK_ALLOW_WRITE_DEBUGFS
> 2. boot with clk_ignore_unused, so clocks stay enabled
> 3. disable clocks via sysfs:
>    echo 1 > /sys/kernel/debug/clk/${CLK}/clk_prepare_enable
>    echo 0 > /sys/kernel/debug/clk/${CLK}/clk_prepare_enable
> 4. check if peripheral is still ok
> 5. repeat step 3 with the next 'interesting' clock

Ah, that makes sense. Thanks.

With that I cannot imagine a scenario that I can only debug with
clk_ignore_unused=n. So let's drop my patch.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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