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

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Date:   Mon, 9 May 2022 14:56:18 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, <agross@...nel.org>,
        <airlied@...ux.ie>, <bjorn.andersson@...aro.org>,
        <daniel@...ll.ch>, <dianders@...omium.org>,
        <dmitry.baryshkov@...aro.org>, <robdclark@...il.com>,
        <sean@...rly.run>, <vkoul@...nel.org>
CC:     <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] drm/msm/dp: Always clear mask bits to disable interrupts
 at dp_ctrl_reset_irq_ctrl()


On 5/6/2022 5:29 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-05-06 14:41:07)
>> dp_catalog_ctrl_reset() will software reset DP controller. But it will
>> not reset programmable registers to default value. DP driver still have
>> to clear mask bits to interrupt status registers to disable interrupts
>> after software reset of controller. This patch removes the enable flag
>> condition checking to always clear mask bits of interrupt status
>> registers to disable interrupts if enable flag is false.
> Another paragraph is needed which is that this (partially?) fixes the
> suspend path where we call dp_catalog_ctrl_reset() but the irq is still
> unmasked and can come in while we're suspending. This leads to bus hangs
> if the irq is handled after we power down the DP hardware because we run
> the irq handler and access a device register assuming that no irq could
> ever come in if we powered down the device. We don't know when the irq
> will be handled though, so it's possible the irq is pending from before
> we disable the irq in the hardware. Don't we need some irq synchronize
> to make sure it doesn't run?

Since irqs are converted into events and executed in event thread 
context, as long as no irq disabled then event q will be emptied 
accordingly.

Also, i think synchronize_irq() have higher risk of deadlocking if 
resources are hold by others.

>> Fixes: ba0a422be723 ("drm/msm/dp: do not initialize phy until plugin interrupt received")
>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_ctrl.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index 38026f2..cbf3399 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -1379,8 +1379,13 @@ 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)
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> a Linux Foundation Collaborative Project
>>