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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 1/2] drm/msm/dsi: Remove spurious IRQF_ONESHOT flag
Date:   Tue,  1 Feb 2022 17:47:32 +0000
Message-Id: <20220201174734.196718-2-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 (and for "normal" kernels
it is a nop). In this case I can find no evidence that suppressing forced
threading is intentional. Had it been intentional then a driver must adopt
the raw_spinlock API in order to avoid deadlocks on PREEMPT_RT kernels
(and avoid calling any kernel API that uses regular spinlocks).

Fix this by removing the spurious additional flag.

This change is required for my Snapdragon 7cx Gen2 tablet to boot-to-GUI
with PREEMPT_RT enabled.

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

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 6b3ced4aaaf5d..3a3f53f0c8ae1 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1877,7 +1877,7 @@ int msm_dsi_host_init(struct msm_dsi *msm_dsi)
 
 	/* do not autoenable, will be enabled later */
 	ret = devm_request_irq(&pdev->dev, msm_host->irq, dsi_host_irq,
-			IRQF_TRIGGER_HIGH | IRQF_ONESHOT | IRQF_NO_AUTOEN,
+			IRQF_TRIGGER_HIGH | IRQF_NO_AUTOEN,
 			"dsi_isr", msm_host);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to request IRQ%u: %d\n",
-- 
2.34.1