linux-kernel - Re: [PATCH] drm/msm/dp: Always clear mask bits to disable interrupts at dp_ctrl_reset_irq

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Message-ID: <CAE-0n52HvhT_RFbJHhijKCCt8jQM70fo6ceAbnYEfOfO-dRxVA@mail.gmail.com>
Date:   Fri, 6 May 2022 20:29:34 -0400
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, dmitry.baryshkov@...aro.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: Always clear mask bits to disable interrupts
 at dp_ctrl_reset_irq_ctrl()

Quoting Kuogee Hsieh (2022-05-06 14:41:07)
> dp_catalog_ctrl_reset() will software reset DP controller. But it will
> not reset programmable registers to default value. DP driver still have
> to clear mask bits to interrupt status registers to disable interrupts
> after software reset of controller. This patch removes the enable flag
> condition checking to always clear mask bits of interrupt status
> registers to disable interrupts if enable flag is false.

Another paragraph is needed which is that this (partially?) fixes the
suspend path where we call dp_catalog_ctrl_reset() but the irq is still
unmasked and can come in while we're suspending. This leads to bus hangs
if the irq is handled after we power down the DP hardware because we run
the irq handler and access a device register assuming that no irq could
ever come in if we powered down the device. We don't know when the irq
will be handled though, so it's possible the irq is pending from before
we disable the irq in the hardware. Don't we need some irq synchronize
to make sure it doesn't run?

>
> Fixes: ba0a422be723 ("drm/msm/dp: do not initialize phy until plugin interrupt received")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 38026f2..cbf3399 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1379,8 +1379,13 @@ void dp_ctrl_reset_irq_ctrl(struct dp_ctrl *dp_ctrl, bool enable)
>
>         dp_catalog_ctrl_reset(ctrl->catalog);
>
> -       if (enable)
> -               dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
> +       /*
> +        * all dp controller programmable registers will not
> +        * be reset to default value after DP_SW_RESET
> +        * therefore interrupt mask bits have to be updated
> +        * to enable/disable interrupts
> +        */
> +       dp_catalog_ctrl_enable_irq(ctrl->catalog, enable);
>  }
>
>  void dp_ctrl_phy_init(struct dp_ctrl *dp_ctrl)
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>