linux-kernel - Re: [PATCH 2/3] drm/ingenic: Reset pixclock rate when parent clock rate changes

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Date:   Tue, 13 Oct 2020 16:17:55 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        od@...c.me, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 2/3] drm/ingenic: Reset pixclock rate when parent clock rate changes

Quoting Paul Cercueil (2020-09-25 05:29:12)
> >>  +static int ingenic_drm_update_pixclk(struct notifier_block *nb,
> >>  +                                unsigned long action,
> >>  +                                void *data)
> >>  +{
> >>  +   struct ingenic_drm *priv = drm_nb_get_priv(nb);
> >>  +
> >>  +   switch (action) {
> >>  +   case PRE_RATE_CHANGE:
> >>  +           mutex_lock(&priv->clk_mutex);
> >>  +           priv->update_clk_rate = true;
> >>  +           drm_crtc_wait_one_vblank(&priv->crtc);
> >>  +           return NOTIFY_OK;
> >>  +   default:
> >>  +           mutex_unlock(&priv->clk_mutex);
> > Any risk the POST_RATE_CHANGE or ABORT_RATE_CHANGE may go missing so 
> > we
> > fail to unlock the mutex?
> > I think not but wanted to make sure you had thought about it.
> 
> My assumption was that you always get POST_RATE_CHANGE or 
> ABORT_RATE_CHANGE. But I am not 100% sure about that.
> 
> Michael, Stephen: is it safe to assume that I will always get notified 
> with POST_RATE_CHANGE or ABORT_RATE_CHANGE, after I got notified with 
> PRE_RATE_CHANGE?
> 

I think one or the other will happen. Of course, the notifiers are sort
of shunned so if you can avoid using notifiers entirely it would be
better.