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

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Message-ID: <d9ac1cee-d4fc-09ae-b2df-82ae2ecd57fb@linaro.org>
Date:   Thu, 31 Mar 2022 13:10:27 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     "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

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);

> 
> 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