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From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc:     Daniel Thompson <daniel.thompson@linaro.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, linux-arm-msm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/2] drm/msm/hdmi: Remove spurious IRQF_ONESHOT flag
Date:   Tue,  1 Feb 2022 17:47:33 +0000
Message-Id: <20220201174734.196718-3-daniel.thompson@linaro.org>
In-Reply-To: <20220201174734.196718-1-daniel.thompson@linaro.org>
References: <20220201174734.196718-1-daniel.thompson@linaro.org>
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Quoting the header comments, IRQF_ONESHOT is "Used by threaded interrupts
which need to keep the irq line disabled until the threaded handler has
been run.". When applied to an interrupt that doesn't request a threaded
irq then IRQF_ONESHOT has a lesser known (undocumented?) side effect,
which it to disable the forced threading of irqs. For "normal" kernels
if there is no thread_fn then IRQF_ONESHOT is a nop.

In this case disabling forced threading is not appropriate because the
driver calls wake_up_all() (via msm_hdmi_i2c_irq) and also directly uses
the regular spinlock API for locking (in msm_hdmi_hdcp_irq() ). Neither
of these APIs can be called from no-thread interrupt handlers on
PREEMPT_RT systems.

Fix this by removing IRQF_ONESHOT.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
 drivers/gpu/drm/msm/hdmi/hdmi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/msm/hdmi/hdmi.c b/drivers/gpu/drm/msm/hdmi/hdmi.c
index 719720709e9e7..e167817b42958 100644
--- a/drivers/gpu/drm/msm/hdmi/hdmi.c
+++ b/drivers/gpu/drm/msm/hdmi/hdmi.c
@@ -306,7 +306,7 @@ int msm_hdmi_modeset_init(struct hdmi *hdmi,
 	}
 
 	ret = devm_request_irq(&pdev->dev, hdmi->irq,
-			msm_hdmi_irq, IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
+			msm_hdmi_irq, IRQF_TRIGGER_HIGH,
 			"hdmi_isr", hdmi);
 	if (ret < 0) {
 		DRM_DEV_ERROR(dev->dev, "failed to request IRQ%u: %d\n",
-- 
2.34.1