linux-kernel - Re: [PATCH] usb: typec: ucsi: Clear pending after acking connector change

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Date:   Tue, 18 May 2021 16:21:37 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Berg <bberg@...hat.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: ucsi: Clear pending after acking connector
 change

On Sat, May 15, 2021 at 09:09:53PM -0700, Bjorn Andersson wrote:
> It's possible that the interrupt handler for the UCSI driver signals a
> connector changes after the handler clears the PENDING bit, but before
> it has sent the acknowledge request. The result is that the handler is
> invoked yet again, to ack the same connector change.
> 
> At least some versions of the Qualcomm UCSI firmware will not handle the
> second - "spurious" - acknowledgment gracefully. So make sure to not
> clear the pending flag until the change is acknowledged.
> 
> Any connector changes coming in after the acknowledgment, that would
> have the pending flag incorrectly cleared, would afaict be covered by
> the subsequent connector status check.
> 
> Fixes: 217504a05532 ("usb: typec: ucsi: Work around PPM losing change information")
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  drivers/usb/typec/ucsi/ucsi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> index 282c3c825c13..f451ce0132a9 100644
> --- a/drivers/usb/typec/ucsi/ucsi.c
> +++ b/drivers/usb/typec/ucsi/ucsi.c
> @@ -694,8 +694,8 @@ static void ucsi_handle_connector_change(struct work_struct *work)
>  	ucsi_send_command(con->ucsi, command, NULL, 0);
>  
>  	/* 3. ACK connector change */
> -	clear_bit(EVENT_PENDING, &ucsi->flags);
>  	ret = ucsi_acknowledge_connector_change(ucsi);
> +	clear_bit(EVENT_PENDING, &ucsi->flags);
>  	if (ret) {
>  		dev_err(ucsi->dev, "%s: ACK failed (%d)", __func__, ret);
>  		goto out_unlock;
> -- 
> 2.29.2

-- 
heikki