linux-kernel - Re: [PATCH v5] drm/msm/dp: Always clear mask bits to disable interrupts at dp_ctrl_reset_irq

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Message-ID: <CAA8EJppc9d+FjVzAX_KU2-akTc1vSmSHMeKr8dp2ynH2LLOyBQ@mail.gmail.com>
Date:   Thu, 12 May 2022 04:03:51 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org, quic_abhinavk@...cinc.com,
        quic_aravindh@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] drm/msm/dp: Always clear mask bits to disable
 interrupts at dp_ctrl_reset_irq_ctrl()

On Thu, 12 May 2022 at 04:01, Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Dmitry Baryshkov (2022-05-11 17:41:50)
> > On 12/05/2022 03:02, Kuogee Hsieh wrote:
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > index af7a80c..f3e333e 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > > @@ -1389,8 +1389,13 @@ void dp_ctrl_reset_irq_ctrl(struct dp_ctrl *dp_ctrl, bool enable)
> > >
> > >       dp_catalog_ctrl_reset(ctrl->catalog);
> > >
> > > -     if (enable)
> > > -             dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
> > > +     /*
> > > +      * all dp controller programmable registers will not
> > > +      * be reset to default value after DP_SW_RESET
> > > +      * therefore interrupt mask bits have to be updated
> > > +      * to enable/disable interrupts
> > > +      */
> > > +     dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
> > >   }
> > >
> > >   void dp_ctrl_phy_init(struct dp_ctrl *dp_ctrl)
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > > index c388323..79439b8 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > > @@ -98,6 +98,8 @@ struct dp_display_private {
> > >       struct dp_ctrl    *ctrl;
> > >       struct dp_debug   *debug;
> > >
> > > +     atomic_t suspended;
> >
> > I think it'd be better to protect it with event_lock rather than using
> > atomics.
>
> Agreed. I think the concern is that the event queue will have "stuff" in
> it. If the event queue was all a threaded irq we could simply call
> synchronize_irq() after disabling the irq bit in the DP hardware and
> then we would know it is safe to power down the DP logic. Unfortunately
> the event queue is a kthread so we can't do that and we have to rewrite
> synchronize_irq() by checking that the event queue is empty and waiting
> for it to empty out otherwise. It's not safe enough to simply do the
> power operations underneath the event_lock because there's a queue in
> the kthread that might be waiting to grab the event_lock to process.

This sounds like a good reason to rewrite event_thread to use
threaded_irq and/or workqueue.

-- 
With best wishes
Dmitry