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Subject: Re: [PATCH 1/5] ACPI: battery: Do not unload battery hooks on single
 error
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>
Cc:     Mark Gross <markgross@kernel.org>, Len Brown <lenb@kernel.org>,
        Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        Matan Ziv-Av <matan@svgalib.org>,
        Corentin Chary <corentin.chary@gmail.com>,
        Jeremy Soller <jeremy@system76.com>, productdev@system76.com,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20220912125342.7395-1-W_Armin@gmx.de>
 <20220912125342.7395-2-W_Armin@gmx.de>
 <f8fa6d10-6eb1-7fa7-80eb-ea190d29ba4a@redhat.com>
 <CAJZ5v0jWVMMTjc+KtBRS86f8kYpbPcDCH9JV2ZgeN4f-MSO8rQ@mail.gmail.com>
From:   Armin Wolf <W_Armin@gmx.de>
Message-ID: <f2af5d01-a2cd-ae96-24c7-d61f5f0d0bc3@gmx.de>
Date:   Mon, 19 Sep 2022 21:12:00 +0200
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Am 19.09.22 um 18:27 schrieb Rafael J. Wysocki:

> On Mon, Sep 19, 2022 at 12:42 PM Hans de Goede <hdegoede@redhat.com> wrote:
>> Hi,
>>
>> On 9/12/22 13:53, Armin Wolf wrote:
>>> Currently, battery hooks are being unloaded if they return
>>> an error when adding a single battery.
>>> This however also causes the removal of successfully added
>>> hooks if they return -ENODEV for a single unsupported
>>> battery.
>>>
>>> Do not unload battery hooks in such cases since the hook
>>> handles any cleanup actions.
>>>
>>> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
>> Maybe instead of removing all error checking, allow -ENODEV
>> and behave as before when the error is not -ENODEV ?
>>
>> Otherwise we should probably make the add / remove callbacks
>> void to indicate that any errors are ignored.
>>
>> Rafael, do you have any opinion on this?
> IMV this is not a completely safe change, because things may simply
> not work in the cases in which an error is returned.
>
> It would be somewhat better to use a special error code to indicate
> "no support" (eg. -ENOTSUPP) and ignore that one only.

I would favor -ENODEV then, since it is already used by quiet a few drivers
to indicate a unsupported battery.

Armin Wolf

>>> ---
>>>   drivers/acpi/battery.c | 24 +++---------------------
>>>   1 file changed, 3 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
>>> index 306513fec1e1..e59c261c7c59 100644
>>> --- a/drivers/acpi/battery.c
>>> +++ b/drivers/acpi/battery.c
>>> @@ -724,20 +724,10 @@ void battery_hook_register(struct acpi_battery_hook *hook)
>>>         * its attributes.
>>>         */
>>>        list_for_each_entry(battery, &acpi_battery_list, list) {
>>> -             if (hook->add_battery(battery->bat)) {
>>> -                     /*
>>> -                      * If a add-battery returns non-zero,
>>> -                      * the registration of the extension has failed,
>>> -                      * and we will not add it to the list of loaded
>>> -                      * hooks.
>>> -                      */
>>> -                     pr_err("extension failed to load: %s", hook->name);
>>> -                     __battery_hook_unregister(hook, 0);
>>> -                     goto end;
>>> -             }
>>> +             hook->add_battery(battery->bat);
>>>        }
>>>        pr_info("new extension: %s\n", hook->name);
>>> -end:
>>> +
>>>        mutex_unlock(&hook_mutex);
>>>   }
>>>   EXPORT_SYMBOL_GPL(battery_hook_register);
>>> @@ -762,15 +752,7 @@ static void battery_hook_add_battery(struct acpi_battery *battery)
>>>         * during the battery module initialization.
>>>         */
>>>        list_for_each_entry_safe(hook_node, tmp, &battery_hook_list, list) {
>>> -             if (hook_node->add_battery(battery->bat)) {
>>> -                     /*
>>> -                      * The notification of the extensions has failed, to
>>> -                      * prevent further errors we will unload the extension.
>>> -                      */
>>> -                     pr_err("error in extension, unloading: %s",
>>> -                                     hook_node->name);
>>> -                     __battery_hook_unregister(hook_node, 0);
>>> -             }
>>> +             hook_node->add_battery(battery->bat);
>>>        }
>>>        mutex_unlock(&hook_mutex);
>>>   }
>>> --
>>> 2.30.2
>>>