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

Greg Kroah-Hartman
2022-02-05T11:53:32Z

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