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 09:36:55 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Chanwoo Choi <cw00.choi@...sung.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

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.

Regards,

Hans