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From:   Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date:   Thu, 31 Mar 2022 14:06:54 +0300
Message-ID: <CAA8EJpooNVxOUa20fACGf3rTVcHBvLKP2=7Eb0x8oxxE7f2iGg@mail.gmail.com>
Subject: Re: [PATCH v6 4/8] drm/msm/dp: avoid handling masked interrupts
To:     Sankeerth Billakanti <sbillaka@qti.qualcomm.com>
Cc:     "Sankeerth Billakanti (QUIC)" <quic_sbillaka@quicinc.com>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
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        "seanpaul@chromium.org" <seanpaul@chromium.org>,
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        quic_kalyant <quic_kalyant@quicinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@quicinc.com>,
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On Thu, 31 Mar 2022 at 14:05, Sankeerth Billakanti
<sbillaka@qti.qualcomm.com> wrote:
>
> Hi Dmitry,
>
> > On 31/03/2022 08:53, Sankeerth Billakanti (QUIC) wrote:
> > > Hi Dmitry,
> > >
> > >> On Wed, 30 Mar 2022 at 19:03, Sankeerth Billakanti
> > >> <quic_sbillaka@quicinc.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@quicinc.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.
> >
> > I see. Maybe the following expression would be better?
> >
> > return isr & (mask & ~DP_DP_HPD_INT_MASK);

Ugh, excuse me please. I meant:

return isr & (mask | ~DP_DP_HPD_INT_MASK);

> >
>
> I believe the confusion occurred because the DP_DP_HPD_STATE_STATUS_CONNECTED and others were defined under the same register definition as REG_DP_DP_HPD_INT_MASK
> I will rearrange the definitions below.
>
> #define REG_DP_DP_HPD_INT_MASK          (0x0000000C)
> #define DP_DP_HPD_PLUG_INT_MASK         (0x00000001)
> #define DP_DP_IRQ_HPD_INT_MASK          (0x00000002)
> #define DP_DP_HPD_REPLUG_INT_MASK       (0x00000004)
> #define DP_DP_HPD_UNPLUG_INT_MASK       (0x00000008)
> #define DP_DP_HPD_INT_MASK              (DP_DP_HPD_PLUG_INT_MASK | \
>                                                 DP_DP_IRQ_HPD_INT_MASK | \
>                                                 DP_DP_HPD_REPLUG_INT_MASK | \
>                                                 DP_DP_HPD_UNPLUG_INT_MASK)
>
> Below are status bits from register REG_DP_DP_HPD_INT_STATUS
>
> #define DP_DP_HPD_STATE_STATUS_CONNECTED        (0x40000000)
> #define DP_DP_HPD_STATE_STATUS_PENDING          (0x20000000)
> #define DP_DP_HPD_STATE_STATUS_DISCONNECTED     (0x00000000)
> #define DP_DP_HPD_STATE_STATUS_MASK             (0xE0000000)
>
> DP_DP_HPD_INT_MASK is 0xF and scope of mask variable is also 0xF (bits 3:0), mask & ~DP_DP_HPD_INT_MASK is 0 always.
>
> For DP, we want to enable all interrupts.
> So the programmed mask value is 0xF. We want to return 0x40000001 for connect and 8 for disconnect
>
> For eDP, we want to disable the connect and disconnect interrupts. So, the mask will be 0x6 (i.e. DP_DP_IRQ_HPD_INT_MASK | DP_DP_HPD_REPLUG_INT_MASK)
> We want to return 0x40000000 (or 0x20000000 based on hpd line status) and 0 for eDP connect and disconnect respectively.
>
> > >
> > > 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
> >
> >
> > --
> > With best wishes
> > Dmitry
>
> Thank you,
> Sankeerth


-- 
With best wishes
Dmitry