netdev - Re: [PATCH v8 00/29] Rework the trip points creation

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Date:   Wed, 5 Oct 2022 15:05:41 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rui.zhang@...el.com,
        Broadcom Kernel Team <bcm-kernel-feedback-list@...adcom.com>,
        Support Opensource <support.opensource@...semi.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Andy Gross <agross@...nel.org>,
        Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>, netdev@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-omap@...r.kernel.org, rafael@...nel.org
Subject: Re: [PATCH v8 00/29] Rework the trip points creation


On 05.10.2022 14:37, Daniel Lezcano wrote:
>
> Hi Marek,
>
> On 03/10/2022 23:18, Daniel Lezcano wrote:
>
> [ ... ]
>
>>> I've tested this v8 patchset after fixing the issue with Exynos TMU 
>>> with
>>> https://lore.kernel.org/all/20221003132943.1383065-1-daniel.lezcano@linaro.org/ 
>>>
>>> patch and I got the following lockdep warning on all Exynos-based 
>>> boards:
>>>
>>>
>>> ======================================================
>>> WARNING: possible circular locking dependency detected
>>> 6.0.0-rc1-00083-ge5c9d117223e #12945 Not tainted
>>> ------------------------------------------------------
>>> swapper/0/1 is trying to acquire lock:
>>> c1ce66b0 (&data->lock#2){+.+.}-{3:3}, at: exynos_get_temp+0x3c/0xc8
>>>
>>> but task is already holding lock:
>>> c2979b94 (&tz->lock){+.+.}-{3:3}, at:
>>> thermal_zone_device_update.part.0+0x3c/0x528
>>>
>>> which lock already depends on the new lock.
>>
>> I'm wondering if the problem is not already there and related to 
>> data->lock ...
>>
>> Doesn't the thermal zone lock already prevent racy access to the data 
>> structure?
>>
>> Another question: if the sensor clock is disabled after reading it, 
>> how does the hardware update the temperature and detect the programed 
>> threshold is crossed?
>
> just a gentle ping, as the fix will depend on your answer ;)
>
Sorry, I've been busy with other stuff. I thought I will fix this once I 
find a bit of spare time.

IMHO the clock management is a bit over-engineered, as there is little 
(if any) benefit from such fine grade clock management. That clock is 
needed only for the AHB related part of the TMU (reading/writing the 
registers). The IRQ generation and temperature measurement is clocked 
from so called 'sclk' (special clock).

I also briefly looked at the code and the internal lock doesn't look to 
be really necessary assuming that the thermal core already serializes 
all the calls.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland