linux-kernel - Re: [PATCH v4] drm/msm/dp: Always clear mask bits to disable interrupts at dp_ctrl_reset_irq

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Message-ID: <e12933c9-0439-410b-e691-0fa444c71011@linaro.org>
Date:   Thu, 12 May 2022 00:47:37 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, dianders@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, bjorn.andersson@...aro.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 v4] drm/msm/dp: Always clear mask bits to disable
 interrupts at dp_ctrl_reset_irq_ctrl()

On 12/05/2022 00:40, Kuogee Hsieh wrote:
> 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.
> 
> This patch also will fix the potential problem happen at system suspend where
> dp_ctrl_reset_irq_ctrl() was called to try to disable HPD related irqs but
> the irq is still unmasked unexpectedly

Why is it unmasked? Especially unexpectedly.

> and can come in while system are
> 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.

Please split into two patches.

> 
> Changes in v2:
> -- add more details commit text
> 
> Changes in v3:
> -- add synchrons_irq()
> -- add atomic_t suspended
> 
> Changes in v4:
> -- correct Fixes's commit ID
> 
> Fixes: 989ebe7bc446 ("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 +++++++--
>   drivers/gpu/drm/msm/dp/dp_display.c | 18 ++++++++++++++++++
>   2 files changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index af7a80c..f3e333e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1389,8 +1389,13 @@ 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)
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index c388323..c34dbfc 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -98,6 +98,8 @@ struct dp_display_private {
>   	struct dp_ctrl    *ctrl;
>   	struct dp_debug   *debug;
>   
> +	atomic_t suspended;

Usage of atomic_t signifies that something is wrong here. Bool should be 
enough here.

> +
>   	struct dp_usbpd_cb usbpd_cb;
>   	struct dp_display_mode dp_mode;
>   	struct msm_dp dp_display;
> @@ -187,6 +189,11 @@ static int dp_add_event(struct dp_display_private *dp_priv, u32 event,
>   	int pndx;
>   
>   	spin_lock_irqsave(&dp_priv->event_lock, flag);
> +	if (atomic_read(&dp_priv->suspended)) {
> +		spin_unlock_irqrestore(&dp_priv->event_lock, flag);
> +		return -EPERM;

Why EPERM?

> +	}
> +
>   	pndx = dp_priv->event_pndx + 1;
>   	pndx %= DP_EVENT_Q_MAX;
>   	if (pndx == dp_priv->event_gndx) {
> @@ -454,6 +461,13 @@ static void dp_display_host_deinit(struct dp_display_private *dp)
>   		dp->dp_display.connector_type, dp->core_initialized,
>   		dp->phy_initialized);
>   
> +	if (!dp->core_initialized) {

Can this happen?

> +		DRM_DEBUG_DP("DP core not initialized\n");
> +		return;
> +	}
> +
> +	synchronize_irq(dp->irq);

Why? If you need to run with IRQs disabled, you can use 
suspend_late/early_resume. But generally it should be enough to check 
for the !suspended in the IRQ.

> +
>   	dp_ctrl_reset_irq_ctrl(dp->ctrl, false);
>   	dp_aux_deinit(dp->aux);
>   	dp_power_deinit(dp->power);
> @@ -1362,6 +1376,8 @@ static int dp_pm_resume(struct device *dev)
>   		dp->dp_display.connector_type, dp->core_initialized,
>   		dp->phy_initialized, dp_display->power_on);
>   
> +	atomic_set(&dp->suspended, 0);
> +
>   	/* start from disconnected state */
>   	dp->hpd_state = ST_DISCONNECTED;
>   
> @@ -1431,6 +1447,8 @@ static int dp_pm_suspend(struct device *dev)
>   		dp->dp_display.connector_type, dp->core_initialized,
>   		dp->phy_initialized, dp_display->power_on);
>   
> +	atomic_inc(&dp->suspended);
> +
>   	/* mainlink enabled */
>   	if (dp_power_clk_status(dp->power, DP_CTRL_PM))
>   		dp_ctrl_off_link_stream(dp->ctrl);


-- 
With best wishes
Dmitry