linux-kernel - RE: [PATCH v6 4/8] drm/msm/dp: avoid handling masked interrupts

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Date:   Thu, 31 Mar 2022 05:53:14 +0000
From:   "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
To:     "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "seanpaul@...omium.org" <seanpaul@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "sean@...rly.run" <sean@...rly.run>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>
Subject: RE: [PATCH v6 4/8] drm/msm/dp: avoid handling masked interrupts

Hi Dmitry,

> On Wed, 30 Mar 2022 at 19:03, Sankeerth Billakanti
> <quic_sbillaka@...cinc.com> wrote:
> >
> > The interrupt register will still reflect the connect and disconnect
> > interrupt status without generating an actual HW interrupt.
> > The controller driver should not handle those masked interrupts.
> >
> > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@...cinc.com>
> > ---
> >  drivers/gpu/drm/msm/dp/dp_catalog.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_catalog.c
> > b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > index 3c16f95..1809ce2 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_catalog.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_catalog.c
> > @@ -608,13 +608,14 @@ u32 dp_catalog_hpd_get_intr_status(struct
> > dp_catalog *dp_catalog)  {
> >         struct dp_catalog_private *catalog = container_of(dp_catalog,
> >                                 struct dp_catalog_private, dp_catalog);
> > -       int isr = 0;
> > +       int isr, mask;
> >
> >         isr = dp_read_aux(catalog, REG_DP_DP_HPD_INT_STATUS);
> >         dp_write_aux(catalog, REG_DP_DP_HPD_INT_ACK,
> >                                  (isr & DP_DP_HPD_INT_MASK));
> > +       mask = dp_read_aux(catalog, REG_DP_DP_HPD_INT_MASK);
> >
> > -       return isr;
> > +       return isr & (DP_DP_HPD_STATE_STATUS_MASK | mask);
> 
> I suspect that the logic is inverted here. Shouldn't it be:
> 
> return isr & DP_DP_HPD_STATE_STATUS_MASK & mask;
> 
> ?
> 
 
The value of DP_DP_HPD_STATE_STATUS_MASK is 0xE0000000 and the value of the read
interrupt mask variable could be is 0xF.

The mask value is indicated via the register, REG_DP_DP_HPD_INT_MASK, bits 3:0.
The HPD status is indicated via a different read-only register REG_DP_DP_HPD_INT_STATUS, bits 31:29. 

isr & DP_DP_HPD_STATE_STATUS_MASK & mask, will return 0 always.

> >  }
> >
> >  int dp_catalog_ctrl_get_interrupt(struct dp_catalog *dp_catalog)
> > --
> > 2.7.4
> >
> 
> 
> --
> With best wishes
> Dmitry

Thank you,
Sankeerth