[v2,2/2] drm/msm/dp: Return IRQ_NONE for unhandled interrupts

  If our interrupt handler gets called and we don't really handle the
interrupt then we should return IRQ_NONE. The current interrupt
handler didn't do this, so let's fix it.

NOTE: for some of the cases it's clear that we should return IRQ_NONE
and some cases it's clear that we should return IRQ_HANDLED. However,
there are a few that fall somewhere in between. Specifically, the
documentation for when to return IRQ_NONE vs. IRQ_HANDLED is probably
best spelled out in the commit message of commit d9e4ad5badf4
("Document that IRQ_NONE should be returned when IRQ not actually
handled"). That commit makes it clear that we should return
IRQ_HANDLED if we've done something to make the interrupt stop
happening.

The case where it's unclear is, for instance, in dp_aux_isr() after
we've read the interrupt using dp_catalog_aux_get_irq() and confirmed
that "isr" is non-zero. The function dp_catalog_aux_get_irq() not only
reads the interrupts but it also "ack"s all the interrupts that are
returned. For an "unknown" interrupt this has a very good chance of
actually stopping the interrupt from happening. That would mean we've
identified that it's our device and done something to stop them from
happening and should return IRQ_HANDLED. Specifically, it should be
noted that most interrupts that need "ack"ing are ones that are
one-time events and doing an "ack" is enough to clear them. However,
since these interrupts are unknown then, by definition, it's unknown
if "ack"ing them is truly enough to clear them. It's possible that we
also need to remove the original source of the interrupt. In this
case, IRQ_NONE would be a better choice.

Given that returning an occasional IRQ_NONE isn't the absolute end of
the world, however, let's choose that course of action. The IRQ
framework will forgive a few IRQ_NONE returns now and again (and it
won't even log them, which is why we have to log them ourselves). This
means that if we _do_ end hitting an interrupt where "ack"ing isn't
enough the kernel will eventually detect the problem and shut our
device down.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

(no changes since v1)

 drivers/gpu/drm/msm/dp/dp_aux.c     | 12 +++++++-----
 drivers/gpu/drm/msm/dp/dp_aux.h     |  2 +-
 drivers/gpu/drm/msm/dp/dp_ctrl.c    | 10 ++++++++--
 drivers/gpu/drm/msm/dp/dp_ctrl.h    |  2 +-
 drivers/gpu/drm/msm/dp/dp_display.c |  8 +++++---
 5 files changed, 22 insertions(+), 12 deletions(-)
  

On 1/26/2023 5:09 PM, Douglas Anderson wrote:
> If our interrupt handler gets called and we don't really handle the
> interrupt then we should return IRQ_NONE. The current interrupt
> handler didn't do this, so let's fix it.
>
> NOTE: for some of the cases it's clear that we should return IRQ_NONE
> and some cases it's clear that we should return IRQ_HANDLED. However,
> there are a few that fall somewhere in between. Specifically, the
> documentation for when to return IRQ_NONE vs. IRQ_HANDLED is probably
> best spelled out in the commit message of commit d9e4ad5badf4
> ("Document that IRQ_NONE should be returned when IRQ not actually
> handled"). That commit makes it clear that we should return
> IRQ_HANDLED if we've done something to make the interrupt stop
> happening.
>
> The case where it's unclear is, for instance, in dp_aux_isr() after
> we've read the interrupt using dp_catalog_aux_get_irq() and confirmed
> that "isr" is non-zero. The function dp_catalog_aux_get_irq() not only
> reads the interrupts but it also "ack"s all the interrupts that are
> returned. For an "unknown" interrupt this has a very good chance of
> actually stopping the interrupt from happening. That would mean we've
> identified that it's our device and done something to stop them from
> happening and should return IRQ_HANDLED. Specifically, it should be
> noted that most interrupts that need "ack"ing are ones that are
> one-time events and doing an "ack" is enough to clear them. However,
> since these interrupts are unknown then, by definition, it's unknown
> if "ack"ing them is truly enough to clear them. It's possible that we
> also need to remove the original source of the interrupt. In this
> case, IRQ_NONE would be a better choice.
>
> Given that returning an occasional IRQ_NONE isn't the absolute end of
> the world, however, let's choose that course of action. The IRQ
> framework will forgive a few IRQ_NONE returns now and again (and it
> won't even log them, which is why we have to log them ourselves). This
> means that if we _do_ end hitting an interrupt where "ack"ing isn't
> enough the kernel will eventually detect the problem and shut our
> device down.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>

> ---
>
> (no changes since v1)
>
>   drivers/gpu/drm/msm/dp/dp_aux.c     | 12 +++++++-----
>   drivers/gpu/drm/msm/dp/dp_aux.h     |  2 +-
>   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 10 ++++++++--
>   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  2 +-
>   drivers/gpu/drm/msm/dp/dp_display.c |  8 +++++---
>   5 files changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c b/drivers/gpu/drm/msm/dp/dp_aux.c
> index 84f9e3e5f964..8e3b677f35e6 100644
> --- a/drivers/gpu/drm/msm/dp/dp_aux.c
> +++ b/drivers/gpu/drm/msm/dp/dp_aux.c
> @@ -368,14 +368,14 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux *dp_aux,
>   	return ret;
>   }
>   
> -void dp_aux_isr(struct drm_dp_aux *dp_aux)
> +irqreturn_t dp_aux_isr(struct drm_dp_aux *dp_aux)
>   {
>   	u32 isr;
>   	struct dp_aux_private *aux;
>   
>   	if (!dp_aux) {
>   		DRM_ERROR("invalid input\n");
> -		return;
> +		return IRQ_NONE;
>   	}
>   
>   	aux = container_of(dp_aux, struct dp_aux_private, dp_aux);
> @@ -384,11 +384,11 @@ void dp_aux_isr(struct drm_dp_aux *dp_aux)
>   
>   	/* no interrupts pending, return immediately */
>   	if (!isr)
> -		return;
> +		return IRQ_NONE;
>   
>   	if (!aux->cmd_busy) {
>   		DRM_ERROR("Unexpected DP AUX IRQ %#010x when not busy\n", isr);
> -		return;
> +		return IRQ_NONE;
>   	}
>   
>   	/*
> @@ -420,10 +420,12 @@ void dp_aux_isr(struct drm_dp_aux *dp_aux)
>   		aux->aux_error_num = DP_AUX_ERR_NONE;
>   	} else {
>   		DRM_WARN("Unexpected interrupt: %#010x\n", isr);
> -		return;
> +		return IRQ_NONE;
>   	}
>   
>   	complete(&aux->comp);
> +
> +	return IRQ_HANDLED;
>   }
>   
>   void dp_aux_reconfig(struct drm_dp_aux *dp_aux)
> diff --git a/drivers/gpu/drm/msm/dp/dp_aux.h b/drivers/gpu/drm/msm/dp/dp_aux.h
> index e930974bcb5b..511305da4f66 100644
> --- a/drivers/gpu/drm/msm/dp/dp_aux.h
> +++ b/drivers/gpu/drm/msm/dp/dp_aux.h
> @@ -11,7 +11,7 @@
>   
>   int dp_aux_register(struct drm_dp_aux *dp_aux);
>   void dp_aux_unregister(struct drm_dp_aux *dp_aux);
> -void dp_aux_isr(struct drm_dp_aux *dp_aux);
> +irqreturn_t dp_aux_isr(struct drm_dp_aux *dp_aux);
>   void dp_aux_init(struct drm_dp_aux *dp_aux);
>   void dp_aux_deinit(struct drm_dp_aux *dp_aux);
>   void dp_aux_reconfig(struct drm_dp_aux *dp_aux);
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index dd26ca651a05..1a5377ef1967 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1979,27 +1979,33 @@ int dp_ctrl_off(struct dp_ctrl *dp_ctrl)
>   	return ret;
>   }
>   
> -void dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
> +irqreturn_t dp_ctrl_isr(struct dp_ctrl *dp_ctrl)
>   {
>   	struct dp_ctrl_private *ctrl;
>   	u32 isr;
> +	irqreturn_t ret = IRQ_NONE;
>   
>   	if (!dp_ctrl)
> -		return;
> +		return IRQ_NONE;
>   
>   	ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
>   
>   	isr = dp_catalog_ctrl_get_interrupt(ctrl->catalog);
>   
> +
>   	if (isr & DP_CTRL_INTR_READY_FOR_VIDEO) {
>   		drm_dbg_dp(ctrl->drm_dev, "dp_video_ready\n");
>   		complete(&ctrl->video_comp);
> +		ret = IRQ_HANDLED;
>   	}
>   
>   	if (isr & DP_CTRL_INTR_IDLE_PATTERN_SENT) {
>   		drm_dbg_dp(ctrl->drm_dev, "idle_patterns_sent\n");
>   		complete(&ctrl->idle_comp);
> +		ret = IRQ_HANDLED;
>   	}
> +
> +	return ret;
>   }
>   
>   struct dp_ctrl *dp_ctrl_get(struct device *dev, struct dp_link *link,
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> index 9f29734af81c..c3af06dc87b1 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> @@ -25,7 +25,7 @@ int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>   int dp_ctrl_off_link(struct dp_ctrl *dp_ctrl);
>   int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
>   void dp_ctrl_push_idle(struct dp_ctrl *dp_ctrl);
> -void dp_ctrl_isr(struct dp_ctrl *dp_ctrl);
> +irqreturn_t dp_ctrl_isr(struct dp_ctrl *dp_ctrl);
>   void dp_ctrl_handle_sink_request(struct dp_ctrl *dp_ctrl);
>   struct dp_ctrl *dp_ctrl_get(struct device *dev, struct dp_link *link,
>   			struct dp_panel *panel,	struct drm_dp_aux *aux,
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index bde1a7ce442f..b5343c9f1c1e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1204,7 +1204,7 @@ static int dp_hpd_event_thread_start(struct dp_display_private *dp_priv)
>   static irqreturn_t dp_display_irq_handler(int irq, void *dev_id)
>   {
>   	struct dp_display_private *dp = dev_id;
> -	irqreturn_t ret = IRQ_HANDLED;
> +	irqreturn_t ret = IRQ_NONE;
>   	u32 hpd_isr_status;
>   
>   	if (!dp) {
> @@ -1232,13 +1232,15 @@ static irqreturn_t dp_display_irq_handler(int irq, void *dev_id)
>   
>   		if (hpd_isr_status & DP_DP_HPD_UNPLUG_INT_MASK)
>   			dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
> +
> +		ret = IRQ_HANDLED;
>   	}
>   
>   	/* DP controller isr */
> -	dp_ctrl_isr(dp->ctrl);
> +	ret |= dp_ctrl_isr(dp->ctrl);
>   
>   	/* DP aux isr */
> -	dp_aux_isr(dp->aux);
> +	ret |= dp_aux_isr(dp->aux);
>   
>   	return ret;
>   }