linux-kernel - Re: [PATCH 2/3] thermal: qoriq_thermal: only enable supported sensors

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Date:   Fri, 16 Jun 2023 11:01:59 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Peng Fan <peng.fan@....nxp.com>, Peng Fan <peng.fan@....com>,
        Sebastian Krzyszkowiak <sebastian.krzyszkowiak@...i.sm>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Cc:     "amitk@...nel.org" <amitk@...nel.org>,
        "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Alice Guo <alice.guo@....com>
Subject: Re: [PATCH 2/3] thermal: qoriq_thermal: only enable supported sensors

On 16/06/2023 03:06, Peng Fan wrote:
> 
> 
> On 6/15/2023 9:49 PM, Daniel Lezcano wrote:
>> Caution: This is an external email. Please take care when clicking 
>> links or opening attachments. When in doubt, report the message using 
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>>
>>
>> On 15/06/2023 14:07, Peng Fan wrote:
>>
>> [ ... ]
>>
>>> Per i.MX8MQ Reference manual:
>>> MSITE:
>>> Monitoring site select 0 - 2. By setting the select bit for a 
>>> temperature sensor site,
>>>   it is enabled and included in all monitoring functions. For proper 
>>> operation, this
>>> field should only change when monitoring is
>>> disabled. If no site is selected, site 0 is monitored by default.
>>>
>>> ME: Before enabling the TMU for monitoring, the TMU must be configured,
>>> see section Initialization Information. Failure to properly 
>>> initialize the
>>> configuration table may result in boundedly undefined
>>> behavior.
>>>
>>> So we must set the SITEs bits before enabling ME bit. So set TMR_ME when
>>> each time call invoke mode violates the spec.
>>>
>>> As I understand, change_mode is per zone, which means per msite for TMU,
>>> but TMU_ME is a global gating bit which should not be set before all 
>>> msites
>>> are set.
>>
>> Mmh, IIUC correctly the documentation, it says the monitoring must be
>> disabled when changing the sites. So in the proposed code, we shall
>> disable the TMU, update the site and then enable the TMU.
>>
>> Can you give a try to see if that works? If yes, then can you submit a
>> patch on top of this series. Meanwhile, I'll pick those changes.
> 
> 
> I did a basic test on i.MX8MQ, it seems work. But I still have concern
> because it volitates the spec, need disable TMU before updating MSITE.
> 
> And if we disable TMU when updating MSITE in your patch, there is 
> potential risk that zone0 is reading temperature, while we disable TMU
> and update MSITE for zone1. So zone0 may get invalid temperature because
> TMU is disabled at this window.
> 
> no good idea from my side, unless we keep check TMU_ME when
> getting temperature.

Yeah, that is a good point. We are ending up to do the TMU check in the 
get_temp() any. Thanks for taking the time to look it up.

   -- Daniel

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