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Thu, 30 Jan 2025 02:30:13 -0800 (PST) Message-ID: <6ed7d545-82d7-4bca-95ec-95447586bb58@tuxon.dev> Date: Thu, 30 Jan 2025 12:30:12 +0200 Precedence: bulk X-Mailing-List: linux-clk@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/6] thermal: of: Export non-devres helper to register/unregister thermal zone To: Daniel Lezcano Cc: rafael@kernel.org, rui.zhang@intel.com, lukasz.luba@arm.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, geert+renesas@glider.be, magnus.damm@gmail.com, mturquette@baylibre.com, sboyd@kernel.org, p.zabel@pengutronix.de, ulf.hansson@linaro.org, linux-pm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org, Claudiu Beznea References: <20250103163805.1775705-1-claudiu.beznea.uj@bp.renesas.com> <20250103163805.1775705-3-claudiu.beznea.uj@bp.renesas.com> <65a16c3f-456e-40ec-91b0-afb57269ed46@tuxon.dev> From: Claudiu Beznea Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 30.01.2025 12:07, Daniel Lezcano wrote: > On Thu, Jan 30, 2025 at 11:08:03AM +0200, Claudiu Beznea wrote: >> Hi, Daniel, >> >> On 29.01.2025 19:24, Daniel Lezcano wrote: >>> Hi Claudiu, >>> >>> On Fri, Jan 03, 2025 at 06:38:01PM +0200, Claudiu wrote: >>>> From: Claudiu Beznea >>>> >>>> On the Renesas RZ/G3S (and other Renesas SoCs, e.g., RZ/G2{L, LC, UL}), >>>> clocks are managed through PM domains. These PM domains, registered on >>>> behalf of the clock controller driver, are configured with >>>> GENPD_FLAG_PM_CLK. In most of the Renesas drivers used by RZ SoCs, the >>>> clocks are enabled/disabled using runtime PM APIs. >>>> >>>> During probe, devices are attached to the PM domain controlling their >>>> clocks. Similarly, during removal, devices are 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() >>>> >>>> In the upcoming Renesas RZ/G3S thermal driver, the >>>> struct thermal_zone_device_ops::change_mode API is implemented to >>>> start/stop the thermal sensor unit. Register settings are updated within >>>> the change_mode API. >>>> >>>> In case devres helpers are used for thermal zone register/unregister the >>>> struct thermal_zone_device_ops::change_mode API is invoked when the >>>> driver is unbound. The identified call stack is as follows: >>>> >>>> device_driver_detach() -> >>>> device_release_driver_internal() -> >>>> device_unbind_cleanup() -> >>>> devres_release_all() -> >>>> devm_thermal_of_zone_release() -> >>>> thermal_zone_device_disable() -> >>>> thermal_zone_device_set_mode() -> >>>> rzg3s_thermal_change_mode() >>>> >>>> The device_unbind_cleanup() function is called after the thermal device is >>>> detached from the PM domain (via dev_pm_domain_detach()). >>>> >>>> The rzg3s_thermal_change_mode() implementation calls >>>> pm_runtime_resume_and_get()/pm_runtime_put_autosuspend() before/after >>>> accessing the registers. However, during the unbind scenario, the >>>> devm_thermal_of_zone_release() is invoked after dev_pm_domain_detach(). >>>> Consequently, the clocks are not enabled, as the device is removed from >>>> the PM domain at this time, leading to an Asynchronous SError Interrupt. >>>> The system cannot be used after this. >>> >>> I've been through the driver before responding to this change. What is the >>> benefit of powering down / up (or clock off / on) the thermal sensor when >>> reading the temperature ? >>> >>> I can understand for disable / enable but I don't get for the classic usage >>> where a governor will be reading the temperature regularly. >> >> I tried to be as power saving as possible both at runtime and after the IP >> is not used anymore as the HW manual doesn't mentioned anything about >> accuracy or implications of disabling the IP clock at runtime. We use >> similar approach (of disabling clocks at runtime) for other IPs in the >> RZ/G3S SoC as well. >> >>> >>> Would the IP need some cycles to capture the temperature accurately after the >>> clock is enabled ? >> >> There is nothing about this mentioned about this in the HW manual of the >> RZ/G3S SoC. The only points mentioned are as described in the driver code: >> - wait at least 3us after each IIO channel read >> - wait at least 30us after enabling the sensor >> - wait at least 50us after setting OE bit in TSU_SM >> >> For this I chose to have it implemented as proposed. > > IMO, disabling/enabling the clock between two reads through the pm runtime may > not be a good thing, especially if the system enters a thermal situation where > it has to mitigate. > > Without any testing capturing the temperatures and compare between the always-on > and on/off, it is hard to say if it is true or not. Up to you to test that or > not. If you think it is fine, then let's go with it. I tested it with and w/o the runtime PM and on/off support (so, everything ON from the probe) and the reported temperature values were similar. Thank you, Claudiu > >> If any, the HW manual is available here >> https://www.renesas.com/en/document/mah/rzg3s-group-users-manual-hardware?r=25458591 >> (an archive is here; the manual is in Deliverables/r01uh1014ej0110-rzg3s.pdf) >> >> Thank you for your review, >> Claudiu >> >>> >>>> Add thermal_of_zone_register()/thermal_of_zone_unregister(). These will >>>> be used in the upcomming RZ/G3S thermal driver. >>>> >>>> Signed-off-by: Claudiu Beznea >> >