linux-kernel - Re: [PATCH 2/2] extcon: axp288: Only reschedule charger-detection at boot when a SDP is detected

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Date:   Mon, 15 Jan 2018 18:08:12 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chen-Yu Tsai <wens@...e.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] extcon: axp288: Only reschedule charger-detection
 at boot when a SDP is detected

On 2018년 01월 15일 17:36, Hans de Goede wrote:
> Hi,
> 
> On 15-01-18 06:22, Chanwoo Choi wrote:
>> On 2018년 01월 15일 00:10, Hans de Goede wrote:
>>> The only misdetection which can happen at boot due to data-lines mux issues
>>> is detecting a non SDP as SDP, so we only need to retry if we detect a SDP
>>> on our first detection.
>>>
>>> Note Vbus misdetection is not a problem, as soon as the drivers controlling
>>> the Vbus path set it correctly we will get an interrupt which reschedules
>>> the charger-detection.
>>>
>>> Also update the comment about the re-detection to reflect this.
>>>
>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>>> ---
>>>   drivers/extcon/extcon-axp288.c | 14 +++++++-------
>>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/extcon/extcon-axp288.c b/drivers/extcon/extcon-axp288.c
>>> index 63b99d5becd7..17e6808af0d1 100644
>>> --- a/drivers/extcon/extcon-axp288.c
>>> +++ b/drivers/extcon/extcon-axp288.c
>>> @@ -161,16 +161,16 @@ static void axp288_chrg_detect_complete(struct axp288_extcon_info *info,
>>>       /*
>>>        * We depend on other drivers to do things like mux the data lines,
>>>        * enable/disable vbus based on the id-pin, etc. Sometimes the BIOS has
>>> -     * not set these things up correctly resulting in the initial charger
>>> -     * cable type detection giving a wrong result and we end up not charging
>>> -     * or charging at only 0.5A.
>>> +     * not set these things up correctly resulting in a wrong result for the
>>> +     * initial charger type detection and we end up charging at only 0.5A.
>>>        *
>>> -     * So we schedule a second cable type detection after 2 seconds to
>>> -     * give the other drivers time to load and do their thing.
>>> +     * If our first detect detects an SDP charger-type, we try again after
>>> +     * 2 seconds to give the other drivers time to load and do their thing.
>>>        */
>>>       if (!info->first_detect_done) {
>>> -        queue_delayed_work(system_wq, &info->det_work,
>>> -                   msecs_to_jiffies(2000));
>>> +        if (info->previous_cable == EXTCON_CHG_USB_SDP)
>>> +            queue_delayed_work(system_wq, &info->det_work,
>>> +                       msecs_to_jiffies(2000));
>>>           info->first_detect_done = true;
>>>       }
>>>  
>>
>> I understand why you add the second delayed_work because of dependency
>> of other consumer driver. But, this patch is not proper method. It looks
>> like the workaround.
>>
>> We need to consider the fundamental solution such as using OF graph
>> or sending the pending notification when consumer driver is probed.
> 
> I agree that having some sort of proper probe ordering here would be
> better. But on these ACPI systems that is going to be quite tricky todo,
> since we've no control over the firmware there.
> 
> Note that you've already merged the workaround, this patch merely changes
> the workaround to avoid it in cases where it is not necessary, so I would
> really like to see this get merged.

I merged your patch because I knew this issue related to dependency.

But, I don't want to merge this patch until developing the fundamental
method. All extcon provider driver have the same issue. I'll try to
resolve this issue thro extcon framework.

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics