linux-kernel - Re: [PATCH v2 2/2] drm/msm/hdmi: Remove spurious IRQF

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Message-ID: <32259670-1261-a305-2bcb-57ebde792f24@linaro.org>
Date:   Thu, 10 Feb 2022 01:03:21 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm/msm/hdmi: Remove spurious IRQF_ONESHOT flag

On 01/02/2022 20:47, Daniel Thompson wrote:
> 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@...aro.org>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.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",


-- 
With best wishes
Dmitry