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>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/520660/
Link: https://lore.kernel.org/r/20230126170745.v2.2.I2d7aec2fadb9c237cd0090a47d6a8ba2054bf0f8@changeid
[DB: reformatted commit message to make checkpatch happy]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

1 files changed, 7 insertions, 5 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 @@ exit:
 	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)