linux-kernel - Re: [PATCH v4 4/6] drm/sprd: add Unisoc's drm display controller driver

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Message-ID: <20210415090908.lmu372lzzjb5hz2b@gilmour>
Date:   Thu, 15 Apr 2021 11:09:08 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Kevin Tang <kevin3.tang@...il.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 4/6] drm/sprd: add Unisoc's drm display controller
 driver

Hi,

On Fri, Apr 09, 2021 at 09:35:07PM +0800, Kevin Tang wrote:
> > > > > +     }
> > > > > +
> > > > > +     return MODE_OK;
> > > > > +}
> > > > > +
> > > > > +static void sprd_crtc_atomic_enable(struct drm_crtc *crtc,
> > > > > +                                struct drm_atomic_state *state)
> > > > > +{
> > > > > +     struct sprd_dpu *dpu = to_sprd_crtc(crtc);
> > > > > +
> > > > > +     sprd_dpu_init(dpu);
> > > > > +
> > > > > +     sprd_dpi_init(dpu);
> > > > > +
> > > > > +     enable_irq(dpu->ctx.irq);
> > > >
> > > > Shouldn't this be in enable_vblank? And I would assume that you would
> > > > have the interrupts enabled all the time, but disabled in your device?
> > > >
> > > It seems better to put in enable_vblank, i will try and test it... Thks
> > >
> > >   And I would assume that you would
> > > have the interrupts enabled all the time, but disabled in your device?
> > > [kevin]I don’t quite understand this, can you help me explain it in
> > > detail?
> >
> > You seem to have a register that enables and disables the interrupt in
> > that device. The way we usually deal with them in this case is just to
> > call request_irq in your bind/probe with the interrupts enabled at the
> > controller level, and mask them when needed at the device level by
> > clearing / setting that bit.
> >
>  Yeah, we have display controller interrupts setting and clear register.
> But the interrupts all been enabled in bootloader(eg, lk or uboot),
> if the interrupt handler is active in the probe/bind phase by request_irq,
> but the whole display pipeline is not ready, there maybe have some problems.

It's fairly common to clear / ack the interrupts from the device before
calling request_irq precisely to avoid that issue.

Maxime

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