linux-kernel - Re: [PATCH] extcon: usbc-tusb320: make sure the state is initialized on probe

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Date:   Thu, 30 Jun 2022 08:03:57 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Chanwoo Choi <cwchoi00@...il.com>, linux-kernel@...r.kernel.org
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Michael Auchter <michael.auchter@...com>
Subject: Re: [PATCH] extcon: usbc-tusb320: make sure the state is initialized
 on probe

Hi!

2022-06-29 at 21:54, Chanwoo Choi wrote:
> On 22. 6. 23. 20:21, Peter Rosin wrote:
>> When the port is connected at boot, there is not necessarily
>> an interrupt flagged in the interrupt status register, causing
>> the IRQ handler to bail out early without reading the state when
>> it is invoked directly from probe.
>>
>> Add a flag that overrides the interrupt status register and reads
>> the state regardless during probe.
>>
>> Fixes: 06bc4ca115cd ("extcon: Add driver for TI TUSB320")
>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>> ---
>>  drivers/extcon/extcon-usbc-tusb320.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/extcon/extcon-usbc-tusb320.c b/drivers/extcon/extcon-usbc-tusb320.c
>> index 6ba3d89b106d..bd3645ae0d52 100644
>> --- a/drivers/extcon/extcon-usbc-tusb320.c
>> +++ b/drivers/extcon/extcon-usbc-tusb320.c
>> @@ -55,6 +55,7 @@ struct tusb320_priv {
>>  	struct extcon_dev *edev;
>>  	struct tusb320_ops *ops;
>>  	enum tusb320_attached_state state;
>> +	bool initialized;
>>  };
>>  
>>  static const char * const tusb_attached_states[] = {
>> @@ -195,7 +196,7 @@ static irqreturn_t tusb320_irq_handler(int irq, void *dev_id)
>>  		return IRQ_NONE;
>>  	}
>>  
>> -	if (!(reg & TUSB320_REG9_INTERRUPT_STATUS))
>> +	if (priv->initialized && !(reg & TUSB320_REG9_INTERRUPT_STATUS))
>>  		return IRQ_NONE;

Do not return early if priv->initialized is false. Behave as before if
priv->initialized is true.

>>  
>>  	state = (reg >> TUSB320_REG9_ATTACHED_STATE_SHIFT) &
>> @@ -297,6 +298,8 @@ static int tusb320_extcon_probe(struct i2c_client *client,
>>  		 */
>>  		tusb320_irq_handler(client->irq, priv);
>>  
>> +	priv->initialized = true;
>> +
> 
> After initializing as 'priv->initialized = true', 
> tusb320_irq_handler() is not anymore detecting the external connector changes.

Have you tested the patch and observed the trouble you are reporting, or
have you simply misread the patch?

> 
> If external connector is detached after finished kernel boot,
> how to change the state of external connector by using extcon_set_state()?
> 

If you did test this and there actually is a problem, maybe there should be
READ_ONCE in the irq handler when checking and WRITE_ONCE when assigning
priv->initialized. But if that's really what's going on I'd be surprised
when it's a variable that changes *once* before the interrupt has even
been requested.

Cheers,
Peter