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SubjectRE: [PATCH v4 4/7] typec: tcpm: Add core support for sink side PPS
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On 30 January 2018 12:47, Heikki Krogerus wrote:

> > +static int tcpm_pps_set_op_curr(struct tcpm_port *port, u16 op_curr)
> > +{
> > + unsigned int target_mw;
> > + int ret = 0;
> > +
> > + mutex_lock(&port->swap_lock);
> > + mutex_lock(&port->lock);
> > +
> > + if (!port->pps_data.active) {
> > + ret = -EOPNOTSUPP;
> > + goto port_unlock;
> > + }
> > +
> > + if (port->state != SNK_READY) {
> > + ret = -EAGAIN;
> > + goto port_unlock;
> > + }
> > +
> > + if (op_curr > port->pps_data.max_curr) {
> > + ret = -EINVAL;
> > + goto port_unlock;
> > + }
> > +
> > + target_mw = (op_curr * port->pps_data.out_volt) / 1000;
> > + if (target_mw < port->operating_snk_mw) {
> > + ret = -EINVAL;
> > + goto port_unlock;
> > + }
> > +
> > + reinit_completion(&port->pps_complete);
> > + port->pps_data.op_curr = op_curr;
> > + port->pps_status = 0;
> > + port->pps_pending = true;
> > + tcpm_set_state(port, SNK_NEGOTIATE_PPS_CAPABILITIES, 0);
>
> Why not just take the swap_lock here..

I believe this would result in deadlock. All of the existing uses of swap_lock
acquire it first before the port->lock is then acquired (and vice-versa for
unlock). We don't want the power role to change during this procedure, so we
hold the swap_lock for the whole process. Have a look at tcpm_dr_set() and
tcpm_pr_set() as examples of existing usage.

> > + return ret;
> > +}
> > +
> > +static int tcpm_pps_set_out_volt(struct tcpm_port *port, u16 out_volt)
> > +{
> > + unsigned int target_mw;
> > + int ret = 0;
> > +
> > + mutex_lock(&port->swap_lock);
> > + mutex_lock(&port->lock);
> > +
> > + if (!port->pps_data.active) {
> > + ret = -EOPNOTSUPP;
> > + goto port_unlock;
>
> Or, on top of what I said above, you could actually consider releasing
> the port lock here and just returning. Then you would not need those
> port_unlock and swap_unlock labels at all..
>
> mutex_unlock(&port->lock);
> return -EOPNOTSUPP;

Based on the comment above, I don't think this makes sense as you'd still need
to release the swap_lock as well, so there would be quite a lot of duplicated
code. Would prefer to stick with the present implementation.

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