linux-kernel - Re: [PATCH v3 4/5] drm: xlnx: zynqmp_dpsub: Filter interrupts against mask

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Date: Mon, 5 Feb 2024 09:35:22 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Anatoliy Klymenko <anatoliy.klymenko@....com>
Cc: maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
	michal.simek@....com, dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] drm: xlnx: zynqmp_dpsub: Filter interrupts
 against mask

Hi Anatoliy,

Thank you for the patch.

On Tue, Jan 23, 2024 at 06:54:01PM -0800, Anatoliy Klymenko wrote:
> Filter out status register against the interrupts' mask.
> 
> Some events are being reported via DP status register, even if
> corresponding interrupts have been disabled. One instance of such event
> leads to generation of VBLANK when the driver is in DRM bridge mode,
> which in turn results in NULL pointer dereferencing. We should avoid
> processing such events in an interrupt handler context.
> 
> This problem is less noticeable when the driver operates in DMA mode, as
> in this case we have DRM CRTC object instantiated and DRM framework
> simply discards unwanted VBLANKs in drm_handle_vblank().
> 
> Signed-off-by: Anatoliy Klymenko <anatoliy.klymenko@....com>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> ---
>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index 5a3335e1fffa..9f48e5bbcdec 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1627,7 +1627,14 @@ static irqreturn_t zynqmp_dp_irq_handler(int irq, void *data)
>  	/* clear status register as soon as we read it */
>  	zynqmp_dp_write(dp, ZYNQMP_DP_INT_STATUS, status);
>  	mask = zynqmp_dp_read(dp, ZYNQMP_DP_INT_MASK);
> -	if (!(status & ~mask))
> +
> +	/*
> +	 * Status register may report some events, which corresponding interrupts
> +	 * have been disabled. Filter out those events against interrupts' mask.
> +	 */
> +	status &= ~mask;
> +
> +	if (!status)
>  		return IRQ_NONE;
>  
>  	/* dbg for diagnostic, but not much that the driver can do */

-- 
Regards,

Laurent Pinchart