linux-kernel - Re: [PATCH v5] drm/msm/dp: Always clear mask bits to disable interrupts at dp_ctrl_reset_irq

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Date:   Thu, 12 May 2022 09:02:12 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>
CC:     <agross@...nel.org>, <airlied@...ux.ie>,
        <bjorn.andersson@...aro.org>, <daniel@...ll.ch>,
        <dianders@...omium.org>, <robdclark@...il.com>, <sean@...rly.run>,
        <vkoul@...nel.org>, <quic_abhinavk@...cinc.com>,
        <quic_aravindh@...cinc.com>, <quic_sbillaka@...cinc.com>,
        <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] drm/msm/dp: Always clear mask bits to disable
 interrupts at dp_ctrl_reset_irq_ctrl()


On 5/11/2022 6:03 PM, Dmitry Baryshkov wrote:
> On Thu, 12 May 2022 at 04:01, Stephen Boyd <swboyd@...omium.org> wrote:
>> Quoting Dmitry Baryshkov (2022-05-11 17:41:50)
>>> On 12/05/2022 03:02, Kuogee Hsieh wrote:
>>>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>>>> index af7a80c..f3e333e 100644
>>>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>>>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>>>> @@ -1389,8 +1389,13 @@ void dp_ctrl_reset_irq_ctrl(struct dp_ctrl *dp_ctrl, bool enable)
>>>>
>>>>        dp_catalog_ctrl_reset(ctrl->catalog);
>>>>
>>>> -     if (enable)
>>>> -             dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
>>>> +     /*
>>>> +      * all dp controller programmable registers will not
>>>> +      * be reset to default value after DP_SW_RESET
>>>> +      * therefore interrupt mask bits have to be updated
>>>> +      * to enable/disable interrupts
>>>> +      */
>>>> +     dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
>>>>    }
>>>>
>>>>    void dp_ctrl_phy_init(struct dp_ctrl *dp_ctrl)
>>>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
>>>> index c388323..79439b8 100644
>>>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>>>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>>>> @@ -98,6 +98,8 @@ struct dp_display_private {
>>>>        struct dp_ctrl    *ctrl;
>>>>        struct dp_debug   *debug;
>>>>
>>>> +     atomic_t suspended;
>>> I think it'd be better to protect it with event_lock rather than using
>>> atomics.
>> Agreed. I think the concern is that the event queue will have "stuff" in
>> it. If the event queue was all a threaded irq we could simply call
>> synchronize_irq() after disabling the irq bit in the DP hardware and
>> then we would know it is safe to power down the DP logic. Unfortunately
>> the event queue is a kthread so we can't do that and we have to rewrite
>> synchronize_irq() by checking that the event queue is empty and waiting
>> for it to empty out otherwise. It's not safe enough to simply do the
>> power operations underneath the event_lock because there's a queue in
>> the kthread that might be waiting to grab the event_lock to process.
> This sounds like a good reason to rewrite event_thread to use
> threaded_irq and/or workqueue.

ok, i will do

1) protect suspended flag with event_lock to prevent new event be added

2) disable interrupts

2) wait for event_q empty before turn off power