linux-kernel - Re: [PATCH 5.10 12/25] drm/vc4: hdmi: Make sure the device is powered with CEC

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Date:   Sat, 5 Feb 2022 14:40:37 +0300
From:   Alexey Khoroshilov <khoroshilov@...ras.ru>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org,
        Michael Stapelberg <michael+drm@...pelberg.ch>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH 5.10 12/25] drm/vc4: hdmi: Make sure the device is powered
 with CEC

On 04.02.2022 12:20, Greg Kroah-Hartman wrote:
> From: Maxime Ripard <maxime@...no.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@...r.kernel.org> # 5.10.x
> Cc: <stable@...r.kernel.org> # 5.15.x
> Cc: <stable@...r.kernel.org> # 5.16.x
> Reported-by: Michael Stapelberg <michael+drm@...pelberg.ch>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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(HDMI_CEC_CNTRL_5, 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;
}


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