linux-kernel - Re: [PATCH v3 1/2] iio: adc: rzg2l

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Message-ID: <1100c663-362a-433c-9c70-8435807b29ac@tuxon.dev>
Date: Tue, 4 Mar 2025 10:58:59 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: prabhakar.mahadev-lad.rj@...renesas.com, jic23@...nel.org, lars@...afoo.de
Cc: linux-iio@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v3 1/2] iio: adc: rzg2l_adc: Open a devres group

Hi, Jonathan,

On 24.02.2025 14:06, Claudiu wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> On all systems where the rzg2l_adc driver is used, the ADC clocks are part
> of a PM domain. The code that implements the PM domains support is in
> drivers/clk/renesas/rzg2l-cpg.c, the functions of interest for this commit
> being rzg2l_cpg_attach_dev() and rzg2l_cpg_deattach_dev(). The PM
> domains support is registered with GENPD_FLAG_PM_CLK which, according to
> the documentation, instructs genpd to use the PM clk framework while
> powering on/off attached devices.
> 
> During probe, the ADC device is attached to the PM domain
> controlling the ADC clocks. Similarly, during removal, the ADC device is
> detached from the PM domain.
> 
> The detachment call stack is as follows:
> 
> device_driver_detach() ->
>   device_release_driver_internal() ->
>     __device_release_driver() ->
>       device_remove() ->
>         platform_remove() ->
>           dev_pm_domain_detach()
> 
> During driver unbind, after the ADC device is detached from its PM domain,
> the device_unbind_cleanup() function is called, which subsequently invokes
> devres_release_all(). This function handles devres resource cleanup.
> 
> If runtime PM is enabled via devm_pm_runtime_enable(), the cleanup process
> triggers the action or reset function for disabling runtime PM. This
> function is pm_runtime_disable_action(), which leads to the following call
> stack of interest when called:
> 
> pm_runtime_disable_action() ->
>   pm_runtime_dont_use_autosuspend() ->
>     __pm_runtime_use_autosuspend() ->
>       update_autosuspend() ->
>         rpm_idle()
> 
> The rpm_idle() function attempts to runtime resume the ADC device. However,
> at the point it is called, the ADC device is no longer part of the PM
> domain (which manages the ADC clocks). Since the rzg2l_adc runtime PM
> APIs directly modifies hardware registers, the
> rzg2l_adc_pm_runtime_resume() function is invoked without the ADC clocks
> being enabled. This is because the PM domain no longer resumes along with
> the ADC device. As a result, this leads to system aborts.
> 
> Open a devres group in the driver probe and release it in the driver
> remove. This ensures the runtime PM is disabled (though the devres group)
> after the rzg2l_adc_remove() finishes its execution avoiding the described
> scenario.

Can you please let me know if you consider this approach acceptable?

Thank you,
Claudiu