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

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Date:   Thu, 27 Jan 2022 23:04:44 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        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] drm/msm: Remove spurious IRQF_ONESHOT flags from dsi & hdmi

On Thu, 27 Jan 2022 at 20:04, Daniel Thompson
<daniel.thompson@...aro.org> 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 (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@...aro.org>

Could you please split it into two parts: separate DSI and HDMI patches

> ---
>
> Notes:
>     Just in case anybody asks, yes! I did use coccinelle to do a quick scan
>     for similar issues. I didn't find any other instances in drivers/drm/ .
>
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
>  drivers/gpu/drm/msm/hdmi/hdmi.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> 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",
> diff --git a/drivers/gpu/drm/msm/hdmi/hdmi.c b/drivers/gpu/drm/msm/hdmi/hdmi.c
> index 3acdeae25caf0..a1bfbc4c74bf7 100644
> --- a/drivers/gpu/drm/msm/hdmi/hdmi.c
> +++ b/drivers/gpu/drm/msm/hdmi/hdmi.c
> @@ -301,7 +301,7 @@ 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",
>
> base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
> --
> 2.34.1
>


-- 
With best wishes
Dmitry