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Subject: Re: [PATCH 5.10 12/25] drm/vc4: hdmi: Make sure the device is powered
 with CEC
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Michael Stapelberg <michael+drm@stapelberg.ch>,
        Maxime Ripard <maxime@cerno.tech>
References: <20220204091914.280602669@linuxfoundation.org>
 <20220204091914.688259001@linuxfoundation.org>
 <91a59ee1-cca4-8d0c-4f86-388434eb5a39@ispras.ru> <Yf5lNIJnvhP4ajam@kroah.com>
From:   Alexey Khoroshilov <khoroshilov@ispras.ru>
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Message-ID: <3bfd9b5e-fa3b-047c-044a-051e28b2e863@ispras.ru>
Date:   Sat, 5 Feb 2022 15:04:02 +0300
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On 05.02.2022 14:53, Greg Kroah-Hartman wrote:
> On Sat, Feb 05, 2022 at 02:40:37PM +0300, Alexey Khoroshilov wrote:
>> On 04.02.2022 12:20, Greg Kroah-Hartman wrote:
>>> From: Maxime Ripard <maxime@cerno.tech>
>>>
>>> Commit 20b0dfa86bef0e80b41b0e5ac38b92f23b6f27f9 upstream.
>>>
>>> The original commit depended on a rework commit (724fc856c09e ("drm/vc4:
>>> hdmi: Split the CEC disable / enable functions in two")) that
>>> (rightfully) didn't reach stable.
>>>
>>> However, probably because the context changed, when the patch was
>>> applied to stable the pm_runtime_put called got moved to the end of the
>>> vc4_hdmi_cec_adap_enable function (that would have become
>>> vc4_hdmi_cec_disable with the rework) to vc4_hdmi_cec_init.
>>>
>>> This means that at probe time, we now drop our reference to the clocks
>>> and power domains and thus end up with a CPU hang when the CPU tries to
>>> access registers.
>>>
>>> The call to pm_runtime_resume_and_get() is also problematic since the
>>> .adap_enable CEC hook is called both to enable and to disable the
>>> controller. That means that we'll now call pm_runtime_resume_and_get()
>>> at disable time as well, messing with the reference counting.
>>>
>>> The behaviour we should have though would be to have
>>> pm_runtime_resume_and_get() called when the CEC controller is enabled,
>>> and pm_runtime_put when it's disabled.
>>>
>>> We need to move things around a bit to behave that way, but it aligns
>>> stable with upstream.
>>>
>>> Cc: <stable@vger.kernel.org> # 5.10.x
>>> Cc: <stable@vger.kernel.org> # 5.15.x
>>> Cc: <stable@vger.kernel.org> # 5.16.x
>>> Reported-by: Michael Stapelberg <michael+drm@stapelberg.ch>
>>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>> ---
>>>  drivers/gpu/drm/vc4/vc4_hdmi.c |   27 ++++++++++++++-------------
>>>  1 file changed, 14 insertions(+), 13 deletions(-)
>>>
>>> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
>>> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
>>> @@ -1402,18 +1402,18 @@ static int vc4_hdmi_cec_adap_enable(stru
>>>  	u32 val;
>>>  	int ret;
>>>  
>>> -	ret = pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev);
>>> -	if (ret)
>>> -		return ret;
>>> -
>>> -	val = HDMI_READ(HDMI_CEC_CNTRL_5);
>>> -	val &= ~(VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET |
>>> -		 VC4_HDMI_CEC_CNT_TO_4700_US_MASK |
>>> -		 VC4_HDMI_CEC_CNT_TO_4500_US_MASK);
>>> -	val |= ((4700 / usecs) << VC4_HDMI_CEC_CNT_TO_4700_US_SHIFT) |
>>> -	       ((4500 / usecs) << VC4_HDMI_CEC_CNT_TO_4500_US_SHIFT);
>>> -
>>>  	if (enable) {
>>> +		ret = pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev);
>>> +		if (ret)
>>> +			return ret;
>>> +
>>> +		val = HDMI_READ(HDMI_CEC_CNTRL_5);
>>> +		val &= ~(VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET |
>>> +			 VC4_HDMI_CEC_CNT_TO_4700_US_MASK |
>>> +			 VC4_HDMI_CEC_CNT_TO_4500_US_MASK);
>>> +		val |= ((4700 / usecs) << VC4_HDMI_CEC_CNT_TO_4700_US_SHIFT) |
>>> +			((4500 / usecs) << VC4_HDMI_CEC_CNT_TO_4500_US_SHIFT);
>>> +
>>>  		HDMI_WRITE(HDMI_CEC_CNTRL_5, val |
>>>  			   VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET);
>>>  		HDMI_WRITE(HDMI_CEC_CNTRL_5, val);
>>> @@ -1439,7 +1439,10 @@ static int vc4_hdmi_cec_adap_enable(stru
>>>  		HDMI_WRITE(HDMI_CEC_CPU_MASK_SET, VC4_HDMI_CPU_CEC);
>>>  		HDMI_WRITE(


, val |
>>>  			   VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET);
>>> +
>>> +		pm_runtime_put(&vc4_hdmi->pdev->dev);
>>>  	}
>>> +
>>>  	return 0;
>>>  }
>>>  
>>> @@ -1531,8 +1534,6 @@ static int vc4_hdmi_cec_init(struct vc4_
>>>  	if (ret < 0)
>>>  		goto err_delete_cec_adap;
>>>  
>>> -	pm_runtime_put(&vc4_hdmi->pdev->dev);
>>> -
>>>  	return 0;
>>>  
>>>  err_delete_cec_adap:
>>>
>>>
>>
>> The patch has moved initialization of val local variable into if
>> (enable) branch. But the variable is used in in the else branch as well.
>> As a result we write of its initialized value here:
>>
>>     HDMI_WRITE(HDMI_CEC_CNTRL_5, val |
>>          VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET);
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> static
>> int vc4_hdmi_cec_adap_enable(struct cec_adapter *adap, bool enable)
>> {
>>   struct vc4_hdmi *vc4_hdmi = cec_get_drvdata(adap);
>>   /* clock period in microseconds */
>>   const u32 usecs = 1000000 / CEC_CLOCK_FREQ;
>>   u32 val;
>>   int ret;
>>
>>   if (enable) {
>>     ret = pm_runtime_resume_and_get(&vc4_hdmi->pdev->dev);
>>     if (ret)
>>       return ret;
>>
>>     val = HDMI_READ(HDMI_CEC_CNTRL_5);
>>     .....
>>
>>   } else {
>>     HDMI_WRITE(HDMI_CEC_CPU_MASK_SET, VC4_HDMI_CPU_CEC);
>>     HDMI_WRITE(HDMI_CEC_CNTRL_5, val |  <------------------ UNINIT VALUE
>>          VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET);
>>
>>     pm_runtime_put(&vc4_hdmi->pdev->dev);
>>   }
>>
>>   return 0;
>> }
> 
> So what does this mean?  That this backport is incorrect and should be
> dropped?  Or that the original commit was wrong?  Or something else?
> 
> confused,
> 
> greg k-h
> 

As far as I can see, the upstream commit was correct and the problem is
in the backport. I would suggest to fix it like this:

   } else {
     HDMI_WRITE(HDMI_CEC_CPU_MASK_SET, VC4_HDMI_CPU_CEC);
-     HDMI_WRITE(HDMI_CEC_CNTRL_5, val
+     HDMI_WRITE(HDMI_CEC_CNTRL_5, HDMI_READ(HDMI_CEC_CNTRL_5)
          VC4_HDMI_CEC_TX_SW_RESET | VC4_HDMI_CEC_RX_SW_RESET);

     pm_runtime_put(&vc4_hdmi->pdev->dev);
   }

But I would left it to comment someone who knows this code better.

--
Best regards,
Alexey Khoroshilov
Linux Verification Center, ISPRAS