linux-kernel - Re: [PATCH v12] thermal: drivers: mediatek: Add the Low Voltage Thermal Sensor driver

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Message-ID: <8662c6bd-b32d-3d3d-b3b7-7f4aeb028309@linaro.org>
Date:   Wed, 1 Feb 2023 18:12:51 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Balsam CHIHI <bchihi@...libre.com>
Cc:     daniel.lezcano@...aro.org, angelogioacchino.delregno@...labora.com,
        rafael@...nel.org, amitk@...nel.org, rui.zhang@...el.com,
        matthias.bgg@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, rdunlap@...radead.org,
        ye.xingchen@....com.cn, p.zabel@...gutronix.de,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        khilman@...libre.com, james.lo@...iatek.com,
        rex-bc.chen@...iatek.com
Subject: Re: [PATCH v12] thermal: drivers: mediatek: Add the Low Voltage
 Thermal Sensor driver

On 01/02/2023 17:46, Balsam CHIHI wrote:
>>> +#ifdef CONFIG_MTK_LVTS_THERMAL_DEBUGFS
>>> +
>>> +static struct dentry *root;
>>
>> How do you handle two instances of driver?
> 
> This root node is the topmost directory for debugfs called 'lvts', the
> different driver instances are below this. It is a singleton.

Indeed. What about removal? Aren't you remobing entire directory
structure on first device removal?

(...)

>>> +
>>> +     of_property_for_each_string(np, "nvmem-cell-names", prop, cell_name) {
>>> +             size_t len;
>>> +             u8 *efuse;
>>> +
>>> +             cell = of_nvmem_cell_get(np, cell_name);
>>> +             if (IS_ERR(cell)) {
>>> +                     dev_dbg(dev, "Failed to get cell '%s'\n", cell_name);
>>
>> Is this an error? If so, why debug? dbg is not for errors.
> 
> AFAIK using dev_dbg does not increase ELF size when DEBUG is disabled.
> If this is not a good reason for you, then I will change it to dev_err.

But also dev_dbg are not visible in error or warn level logs. If this is
not an error, then indeed dev_dbg could be fine. But errors should be
verbose.

> 
>>
>>> +                     return PTR_ERR(cell);
>>> +             }
>>> +
>>> +             efuse = nvmem_cell_read(cell, &len);
>>> +
>>> +             nvmem_cell_put(cell);
>>> +
>>> +             if (IS_ERR(efuse)) {
>>> +                     dev_dbg(dev, "Failed to read cell '%s'\n", cell_name);
>>> +                     return PTR_ERR(efuse);
>>> +             }
>>> +
>>> +             lvts_td->calib = devm_krealloc(dev, lvts_td->calib,
>>> +                                            lvts_td->calib_len + len, GFP_KERNEL);
>>> +             if (!lvts_td->calib)
>>> +                     return -ENOMEM;
>>> +
>>> +             memcpy(lvts_td->calib + lvts_td->calib_len, efuse, len);
>>> +
>>> +             lvts_td->calib_len += len;
>>> +
>>> +             kfree(efuse);
>>> +     }
>>> +
>>> +     return 0;
>>> +}
>>> +
>>> +static int __init lvts_golden_temp_init(struct device *dev, u32 *value)
>>
>> You did not test it, right? Build with section mismatch analysis...
> 
> I'm not sure to fully understand this comment.
> Would you explain, please?

git grep -i "section mismatch" leads to lib/Kconfig.debug and
DEBUG_SECTION_MISMATCH

(...)

>>> +static struct lvts_ctrl_data mt8195_lvts_data_ctrl[] = {
>>
>> Why this cannot be const?
> 
> I've got the following warning when I added "const"
> drivers/thermal/mediatek/lvts_thermal.c:1286:27: warning:
> initialization discards ‘const’ qualifier from pointer target type
> [-Wdiscarded-qualifiers]
>  1286 |         .lvts_ctrl      = mt8195_lvts_data_ctrl,
>       |                           ^~~~~~~~~~~~~~~~~~~~~~~~~

As with every const... Do you need lvts_ctrl to be non-const? If yes,
then how do you handle multiple devices (singleton)?

Best regards,
Krzysztof