linux-kernel - Re: [PATCH 2/2] drm/msm/dp: Return IRQ

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Date:   Wed, 25 Jan 2023 10:21:57 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Johan Hovold <johan+linaro@...nel.org>,
        Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
        Sean Paul <sean@...rly.run>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/msm/dp: Return IRQ_NONE for unhandled interrupts

Hi,

On Wed, Jan 25, 2023 at 9:22 AM Kuogee Hsieh <quic_khsieh@...cinc.com> wrote:
>
> > -void dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
> > +irqreturn_t dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
> >   {
> >       struct dp_ctrl_private *ctrl;
> >       u32 isr;
> > +     irqreturn_t ret = IRQ_NONE;
> >
> >       if (!dp_ctrl)
> > -             return;
> > +             return IRQ_NONE;
> >
> >       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
> >
> >       isr = dp_catalog_ctrl_get_interrupt(ctrl->catalog);
> can you add (!isr) check and return IRQ_NONE here to be consistent with
> dp_aux_isr()?

I could, though it doesn't really buy us a whole lot in this case and
just adds an extra test that's not needed. Here it should be easy for
someone reading the function to see that if "isr == 0" that neither of
the two "if" statements below will fire and we'll return "IRQ_NONE"
anyway.

...that actually made me go back and wonder whether we still needed
the "if" test in dp_aux_isr() or if it too was also redundant. It
turns out that it's not! The previous patch made dp_aux_irq() detect
unexpected interrupts. Thus the "if (!isr)" test earlier is important
because otherwise we'd end up WARNing "Unexpected interrupt:
0x00000000" which would be confusing.

So unless you or others feel strongly that I should add the redundant
test here, I'd rather keep it off. Let me know.

-Doug