linux-kernel - Re: usb: typec: ucsi: Clear EVENT_PENDING bit if ucsi_send

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Message-ID: <21d247d3-83be-ba53-c982-2ab0e2e4ffb3@quicinc.com>
Date:   Tue, 12 Sep 2023 16:37:47 +0530
From:   Prashanth K <quic_prashk@...cinc.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "# 5 . 16" <stable@...r.kernel.org>
Subject: Re: usb: typec: ucsi: Clear EVENT_PENDING bit if ucsi_send_command
 fails



On 11-09-23 06:19 pm, Heikki Krogerus wrote:
> On Mon, Sep 11, 2023 at 02:34:15PM +0530, Prashanth K wrote:
>> Currently if ucsi_send_command() fails, then we bail out without
>> clearing EVENT_PENDING flag. So when the next connector change
>> event comes, ucsi_connector_change() won't queue the con->work,
>> because of which none of the new events will be processed.
>>
>> Fix this by clearing EVENT_PENDING flag if ucsi_send_command()
>> fails.
>>
>> Cc: <stable@...r.kernel.org> # 5.16
>> Fixes: 512df95b9432 ("usb: typec: ucsi: Better fix for missing unplug events issue")
>> Signed-off-by: Prashanth K <quic_prashk@...cinc.com>
>> ---
>>   drivers/usb/typec/ucsi/ucsi.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
>> index c6dfe3d..509c67c 100644
>> --- a/drivers/usb/typec/ucsi/ucsi.c
>> +++ b/drivers/usb/typec/ucsi/ucsi.c
>> @@ -884,6 +884,7 @@ static void ucsi_handle_connector_change(struct work_struct *work)
>>   	if (ret < 0) {
>>   		dev_err(ucsi->dev, "%s: GET_CONNECTOR_STATUS failed (%d)\n",
>>   			__func__, ret);
>> +		clear_bit(EVENT_PENDING, &con->ucsi->flags);
>>   		goto out_unlock;
>>   	}
> 
> I think it would be better to just move that label (out_unlock) above
> the point where clear_bit() is already called instead of separately
> calling it like that. That way the Connector Change Event will
> also get acknowledged.
Do we really need to ACK in this case since we didn't process the 
current connector change event
> 
> If this really can happen, then I think it would be good to also
> schedule a task for ucsi_check_connection():
> 
>          if (ret < 0) {
>                  dev_err(ucsi->dev, "%s: GET_CONNECTOR_STATUS failed (%d)\n",
>                          __func__, ret);
> +               ucsi_partner_task(con, ucsi_check_connection, 1, HZ);
>                  goto out_unlock;
>          }
> 
> thanks,
> 
Retrying is a good idea, but ucsi_check_connection() doesn't have the 
full functionality compared to handle_connector_change. I guess 
ucsi_check_connection() will send a set_role, but won't handle the 
connector_change scenarios happening due to PR/DR swap, which will lead 
to deadlocks (due to wait_for_completion). This is just an example. So 
its better to bail out and process the next events, because the failure 
here is from the glink layer.

Thanks
Prashanth K