Re: [PATCH 2/3] usb: typec: ucsi: Move unregister out of atomic section

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

On Sun, Aug 18, 2024 at 04:17:38PM -0700, Bjorn Andersson wrote:
> Commit 'caa855189104 ("soc: qcom: pmic_glink: Fix race during
> initialization")' moved the pmic_glink client list under a spinlock, as
> it is accessed by the rpmsg/glink callback, which in turn is invoked
> from IRQ context.
> 
> This means that ucsi_unregister() is now called from IRQ context, which
> isn't feasible as it's expecting a sleepable context. An effort is under
> way to get GLINK to invoke its callbacks in a sleepable context, but
> until then lets schedule the unregistration.
> 
> A side effect of this is that ucsi_unregister() can now happen
> after the remote processor, and thereby the communication link with it, is
> gone. pmic_glink_send() is amended with a check to avoid the resulting
> NULL pointer dereference, but it becomes expecting to see a failing send
> upon shutting down the remote processor (e.g. during a restart following
> a firmware crash):
> 
>   ucsi_glink.pmic_glink_ucsi pmic_glink.ucsi.0: failed to send UCSI write request: -5
> 
> Fixes: caa855189104 ("soc: qcom: pmic_glink: Fix race during initialization")
> Cc: stable@vger.kernel.org
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>

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

> ---
>  drivers/soc/qcom/pmic_glink.c       | 10 +++++++++-
>  drivers/usb/typec/ucsi/ucsi_glink.c | 28 +++++++++++++++++++++++-----
>  2 files changed, 32 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/soc/qcom/pmic_glink.c b/drivers/soc/qcom/pmic_glink.c
> index 58ec91767d79..e4747f1d3da5 100644
> --- a/drivers/soc/qcom/pmic_glink.c
> +++ b/drivers/soc/qcom/pmic_glink.c
> @@ -112,8 +112,16 @@ EXPORT_SYMBOL_GPL(pmic_glink_register_client);
>  int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len)
>  {
>  	struct pmic_glink *pg = client->pg;
> +	int ret;
>  
> -	return rpmsg_send(pg->ept, data, len);
> +	mutex_lock(&pg->state_lock);
> +	if (!pg->ept)
> +		ret = -ECONNRESET;
> +	else
> +		ret = rpmsg_send(pg->ept, data, len);
> +	mutex_unlock(&pg->state_lock);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(pmic_glink_send);
>  
> diff --git a/drivers/usb/typec/ucsi/ucsi_glink.c b/drivers/usb/typec/ucsi/ucsi_glink.c
> index ac53a81c2a81..a33056eec83d 100644
> --- a/drivers/usb/typec/ucsi/ucsi_glink.c
> +++ b/drivers/usb/typec/ucsi/ucsi_glink.c
> @@ -68,6 +68,9 @@ struct pmic_glink_ucsi {
>  
>  	struct work_struct notify_work;
>  	struct work_struct register_work;
> +	spinlock_t state_lock;
> +	unsigned int pdr_state;
> +	unsigned int new_pdr_state;
>  
>  	u8 read_buf[UCSI_BUF_SIZE];
>  };
> @@ -244,8 +247,22 @@ static void pmic_glink_ucsi_notify(struct work_struct *work)
>  static void pmic_glink_ucsi_register(struct work_struct *work)
>  {
>  	struct pmic_glink_ucsi *ucsi = container_of(work, struct pmic_glink_ucsi, register_work);
> +	unsigned long flags;
> +	unsigned int new_state;
> +
> +	spin_lock_irqsave(&ucsi->state_lock, flags);
> +	new_state = ucsi->new_pdr_state;
> +	spin_unlock_irqrestore(&ucsi->state_lock, flags);
> +
> +	if (ucsi->pdr_state != SERVREG_SERVICE_STATE_UP) {
> +		if (new_state == SERVREG_SERVICE_STATE_UP)
> +			ucsi_register(ucsi->ucsi);
> +	} else {
> +		if (new_state == SERVREG_SERVICE_STATE_DOWN)
> +			ucsi_unregister(ucsi->ucsi);
> +	}
>  
> -	ucsi_register(ucsi->ucsi);
> +	ucsi->pdr_state = new_state;
>  }
>  
>  static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
> @@ -269,11 +286,12 @@ static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
>  static void pmic_glink_ucsi_pdr_notify(void *priv, int state)
>  {
>  	struct pmic_glink_ucsi *ucsi = priv;
> +	unsigned long flags;
>  
> -	if (state == SERVREG_SERVICE_STATE_UP)
> -		schedule_work(&ucsi->register_work);
> -	else if (state == SERVREG_SERVICE_STATE_DOWN)
> -		ucsi_unregister(ucsi->ucsi);
> +	spin_lock_irqsave(&ucsi->state_lock, flags);
> +	ucsi->new_pdr_state = state;
> +	spin_unlock_irqrestore(&ucsi->state_lock, flags);
> +	schedule_work(&ucsi->register_work);
>  }
>  
>  static void pmic_glink_ucsi_destroy(void *data)
> 
> -- 
> 2.34.1

-- 
heikki