linux-kernel - Re: [PATCH 01/10] i2c: add suspended flag and accessors for i2c adapters

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Message-ID: <6fb7d574-9648-2960-5724-8b02a3348012@redhat.com>
Date:   Fri, 21 Dec 2018 11:43:13 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Lukas Wunner <lukas@...ner.de>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/10] i2c: add suspended flag and accessors for i2c
 adapters

Hi,

On 20-12-18 22:09, Rafael J. Wysocki wrote:
> On Thursday, December 20, 2018 11:00:29 AM CET Hans de Goede wrote:
>> Hi,
>>
>> On 19-12-18 23:33, Wolfram Sang wrote:
>>> Hi Lukas, Hans,
>>>
>>> On Wed, Dec 19, 2018 at 07:36:54PM +0100, Hans de Goede wrote:
>>>> Hi,
>>>>
>>>> On 19-12-18 18:22, Lukas Wunner wrote:
>>>>> On Wed, Dec 19, 2018 at 05:48:17PM +0100, Wolfram Sang wrote:
>>>>>> +static inline void i2c_mark_adapter_suspended(struct i2c_adapter *adap)
>>>>>> +{
>>>>>> +	i2c_lock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
>>>>>> +	set_bit(I2C_ALF_IS_SUSPENDED, &adap->locked_flags);
>>>>>> +	i2c_unlock_bus(adap, I2C_LOCK_ROOT_ADAPTER);
>>>>>> +}
>>>>>
>>>>> This looks like a duplication of the is_suspended flag in struct dev_pm_info.
>>>>> Any reason why you can't use that?  If so, it would be good to document the
>>>>> reason in the commit message.
>>>>
>>>> Oh, that is a very good point and that one only gets set on system suspend
>>>> and not on resume suspend, working around the problems with the i2c-designware
>>>
>>> Just to make it clear: you mean runtime suspend, not resume suspend, or?
>>
>> Yes I mean runtime-suspend, sorry.
> 
> The power.is_suspended flag is about system-wide suspend, however.

Right, which is why it is good for us to use, when runtime-suspend the
i2c-adapter drivers transfer function will do a runtime_pm_get and all
is well, we want to check for someone trying to do i2c-transfers on
the adapter while it is system-suspended, since then the runtime_pm_get
is a no-op and things fail.

So for this use case it is a good thing that power.is_suspended flag is about
system-wide suspend (which is what I was trying to say in the first place).

Regards,

Hans