linux-kernel - Re: [PATCH v2 1/2] thermal/drivers/imx_sc: Rely on the platform data to get the resource id

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Message-ID: <17d09638-01e6-038f-c3db-cbe02ccb9327@linaro.org>
Date:   Fri, 26 Aug 2022 00:28:31 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>
Cc:     rafael@...nel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Amit Kucheria <amitk@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] thermal/drivers/imx_sc: Rely on the platform data
 to get the resource id

On 18/08/2022 10:23, Daniel Lezcano wrote:
> Currently the imx_sc driver is reimplementing part of the thermal zone
> parsing from the thermal OF tree code to get the sensor id associated
> with a thermal zone sensor.
> 
> The driver platform specific code should know what sensor is present
> and not rely on the thermal zone description to do a discovery. Well
> that is arguable but all the other drivers have a per platform data
> telling what sensor id to use.
> 
> The imx_sc thermal driver is the only one using a different
> approach. Not invalid but forcing to keep a specific function
> 'thermal_zone_of_get_sensor_id()' to get the sensor id for a specific
> thermal zone as the self-explanatory function tells and having device
> tree code inside the driver.
> 
> The thermal OF code had a rework and remains now self-encapsulated
> with a register/unregister functions and their 'devm' variants, except
> for the function mentioned above.
> 
> After investigating, it appears the imx_sc sensor is defined in
> arch/arm64/boot/dts/freescale/imx8qxp.dtsi:
> 
> which defines the cpu-thermal zone with the id: IMX_SC_R_SYSTEM
> 
> This dtsi is included by:
>   - imx8qxp-ai_ml.dts
>   - imx8qxp-colibri.dtsi
>   - imx8qxp-mek.dts
> 
> The two first ones do not define more thermal zones
> The third one adds the pmic-thermal0 zone with id: IMX_SC_R_PMIC_0
> 
> The thermal OF code returns -ENODEV if the thermal zone registration
> with a specific id fails because the description is not available in
> the DT for such a sensor id. In this case we continue with the other
> ids without bailing out with an error.
> 
> So we can build for the 'fsl,imx-sc-thermal' a compatible data, an
> array of sensor ids containing IMX_SC_R_SYSTEM and IMX_SC_R_PMIC_0.
> 
> The latter won't be found but that will not result in an error but a
> normal case where we continue the initialization with other ids.
> 
> Just to clarify, it is what the thermal framework does and what the
> other drivers are expecting: when a registration fails with -ENODEV
> this is not an error but a case where the description is not found in
> the device tree, that be can the entire thermal zones description or a
> specific thermal zone with an unknown id.
> 
> There is one small functional change but without impact. When there is
> no 'thermal-zones' description the probe function was returning
> '-ENODEV', now it returns zero. When a thermal zone fails to register
> with an error different from '-ENODEV', the error is detected and
> returned.
> 
> Change the code accordingly and remove the OF code from the driver.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
> The changes apply on the linux-next branch:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux.git/log/?h=thermal/linux-next
> 
> I don't have the platform, so I was not able to test the changes.
> 
> Changelog:
>   v2:
>      - Clarified a bit more the changes description
> 
>      - Fix use-after-free and add a couple of comments to reflect the
>       patch description
> 
>      - Put back the error message in case there is an error with the
>        registration
> 

Is there any comment on this change ?



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