linux-kernel - Re: [PATCH] hwmon: (jc42) Restore the min/max/critical temperatures on resume

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Date:   Wed, 19 Oct 2022 15:50:24 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-hwmon@...r.kernel.org, jdelvare@...e.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (jc42) Restore the min/max/critical temperatures
 on resume

On 10/19/22 15:03, Martin Blumenstingl wrote:
> Hi Guenter,
> 
> Thank you for the quick feedback!
> 
> On Wed, Oct 19, 2022 at 11:51 PM Guenter Roeck <linux@...ck-us.net> wrote:
> [...]
>>> +     if (data->valid || data->temp[t_min])
>>
>> This contradicts "with applying the previous values by only configuring
>> them if they are known valid". It explicitly applies the values if they
>> are marked as not valid, and it also applies the values if they are 0
>> (I don't really see the value of doing that).
>>
>> Sorry, I don't understand the logic. Did you mean to use "&&" instead
>> of "||" ?
> My understanding is that that:
> 1) data->valid = true is only set in jc42_update_device() (which is
> only called when reading back the values from the registers)
> 2) jc42_write() can write values without setting data->value = true
> In other words: if jc42_read() is never called but jc42_write() is
> then we still have some setting to apply while data->valid is false.
> Whether that's possible in reality is something that I'm not sure
> about.
> 

The above only means that the code is not optimized for the problem
you are trying to solve.

- Calling jc42_update_device() would solve the valid problem.
- Calling jc42_update_device() from the write function would
   solve it as well.

Relying on a previous call to the write function is most definitely
wrong.

Also, for optimization, jc42_update_device() should really read the limit
registers only once. The best solution would probably be to convert the
driver to use regmap and let regmap handle the caching.

Guenter

> If your suggestion is to simplify this to use data->valid only then I
> can do that.
> It would be great if you could also comment on whether
> jc42_update_device() should be called from jc42_suspend() to give the
> driver the chance to at least read the data once (and set data->valid)
> if this has not happened before.
> 
> 
> Best regards,
> Martin