linux-kernel - Re: [PATCH] drm/atmel-hlcdc: prevent divide by zero

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Message-ID: <20190109101224.GT21184@phenom.ffwll.local>
Date:   Wed, 9 Jan 2019 11:12:24 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Peter Rosin <peda@...ntia.se>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drm/atmel-hlcdc: prevent divide by zero

On Tue, Jan 08, 2019 at 12:31:36PM +0000, Peter Rosin wrote:
> While trying to temporarily hide a plane, one thing that was attempted
> was to call (from libdrm)
> 
> 	drmModeSetPlane(fd, plane_id, crtc_id, fb_id, 0,
> 			0, 0, 0, 0, 0, 0, 0, 0);
> 
> This call causes a pair of "Division by zero in kernel." messages. Kill
> those messages, but preserve the current behaviour that also happen to
> make the plane disappear with the above call.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> Side note, when comparing with drm_atomic_helper_check_plane_state(), I get
> the feeling that the src rect should be clipped together with the crtc rect
> if/when clipping is needed. That function calls drm_rect_clip_scaled(), and
> the equivalent does not seem to happen here. Should clipping be performed
> on the src rect?

Any reasons atmel can't switch over to that helper? Would compute a nice
->visible state variable for you ...
-Daniel

> 
> Cheers,
> Peter
> 
> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> index 3cc489b870fe..1bdb30dc218c 100644
> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c
> @@ -675,10 +675,16 @@ static int atmel_hlcdc_plane_atomic_check(struct drm_plane *p,
>  		state->crtc_y = 0;
>  	}
>  
> -	patched_src_w = DIV_ROUND_CLOSEST(patched_crtc_w * state->src_w,
> -					  state->crtc_w);
> -	patched_src_h = DIV_ROUND_CLOSEST(patched_crtc_h * state->src_h,
> -					  state->crtc_h);
> +	if (state->crtc_w)
> +		patched_src_w = DIV_ROUND_CLOSEST(patched_crtc_w * state->src_w,
> +						  state->crtc_w);
> +	else
> +		patched_src_w = 0;
> +	if (state->crtc_h)
> +		patched_src_h = DIV_ROUND_CLOSEST(patched_crtc_h * state->src_h,
> +						  state->crtc_h);
> +	else
> +		patched_src_h = 0;
>  
>  	hsub = drm_format_horz_chroma_subsampling(fb->format->format);
>  	vsub = drm_format_vert_chroma_subsampling(fb->format->format);
> -- 
> 2.11.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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