linux-kernel - Re: [PATCH] mailbox: txdone_method shouldn't always be reset

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Date:   Thu, 16 Nov 2017 23:04:00 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Klimov <alexey.klimov@....com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH] mailbox: txdone_method shouldn't always be reset

On Thu 16 Nov 22:47 PST 2017, Jassi Brar wrote:
> On 16 Nov 2017 23:12, "Bjorn Andersson" <bjorn.andersson@...aro.org> wrote:
> On Thu 16 Nov 09:06 PST 2017, Jassi Brar wrote:
> > diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> > index 674b35f..95e480e 100644
> > --- a/drivers/mailbox/mailbox.c
> > +++ b/drivers/mailbox/mailbox.c
> > @@ -124,7 +124,8 @@ static enum hrtimer_restart txdone_hrtimer(struct
> > hrtimer *hrtimer)
> >         for (i = 0; i < mbox->num_chans; i++) {
> >                 struct mbox_chan *chan = &mbox->chans[i];
> >
> > -               if (chan->active_req && chan->cl) {
> > +               if (chan->active_req && chan->cl &&
> > +                   chan->txdone_method == TXDONE_BY_POLL) {
> 
> The hrtimer code will crash before reaching this point if the channel
> wasn't TXDONE_BY_POLL when it was created, so this part is not needed.
> 
> 
> We have one timer for all channels of a controller. While this channel may
> be run by ACK, some other might need to be POLLed. And we want to avoid
> polling this channel.
> 

Oh, you're right.

But the fact that the timer function will poll channels that are
"upgraded" to ACK is a separate issue.

> 
> >                         txdone = chan->mbox->ops->last_tx_done(chan);
> >                         if (txdone)
> >                                 tx_tick(chan, 0);
> > @@ -418,7 +419,7 @@ void mbox_free_channel(struct mbox_chan *chan)
> >         spin_lock_irqsave(&chan->lock, flags);
> >         chan->cl = NULL;
> >         chan->active_req = NULL;
> > -       if (chan->txdone_method == TXDONE_BY_ACK)
> > +       if (chan->txdone_method == TXDONE_BY_ACK &&
> chan->mbox->txdone_poll)
> 
> This should be enough, but the logic here is not obvious. This relies on
> the fact that a mbox with txdone_poll would have been initialized as
> txdone = POLL and that txdone now being ACK would imply that it was
> "upgraded" in the request path.
> 
> So at least this would have to be captured in a comment.
> 
> 
> Sure I'll add a comment.
> 

Thanks

Regards,
Bjorn