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Date:   Sat, 5 Feb 2022 12:53:24 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Alexey Khoroshilov <khoroshilov@ispras.ru>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Michael Stapelberg <michael+drm@stapelberg.ch>,
        Maxime Ripard <maxime@cerno.tech>
Subject: Re: [PATCH 5.10 12/25] drm/vc4: hdmi: Make sure the device is
 powered with CEC
Message-ID: <Yf5lNIJnvhP4ajam@kroah.com>
References: <20220204091914.280602669@linuxfoundation.org>
 <20220204091914.688259001@linuxfoundation.org>
 <91a59ee1-cca4-8d0c-4f86-388434eb5a39@ispras.ru>
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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(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;
> }

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