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

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Date:   Thu, 31 Mar 2022 11:04:59 +0000
From:   Sankeerth Billakanti <sbillaka@....qualcomm.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 31/03/2022 08:53, Sankeerth Billakanti (QUIC) wrote:
> > 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.
> 
> I see. Maybe the following expression would be better?
> 
> 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