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

Alexey Khoroshilov
2022-02-05T11:40:44Z

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;
}

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