Re: [PATCH 06/10] drm/tegra: Handle 64-bit return from drm_crtc_vblank_count()

From: "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>
To: "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>
Cc: "treding@nvidia.com" <treding@nvidia.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"Vivi, Rodrigo" <rodrigo.vivi@intel.com>
Subject: Re: [PATCH 06/10] drm/tegra: Handle 64-bit return from drm_crtc_vblank_count()
Date: Wed, 7 Feb 2018 01:41:18 +0000	[thread overview]
Message-ID: <1517969059.11349.39.camel@dk-H97M-D3H> (raw)
In-Reply-To: <20180203051302.9974-6-dhinakaran.pandiyan@intel.com>

On Fri, 2018-02-02 at 21:12 -0800, Dhinakaran Pandiyan wrote:
> 570e86963a51 ("drm: Widen vblank count to 64-bits [v3]") changed the
> return type for drm_crtc_vblank_count() to u64. This could cause
> potential problems if the return value is used in arithmetic operations
> with a 32-bit reference HW vblank count. Explicitly typecasting this
> down to u32 either fixes a potential problem or serves to add clarity in
> case the implicit typecasting was already correct.
> 
> Cc: Keith Packard <keithp@keithp.com>
> Cc: Thierry Reding <treding@nvidia.com>

Thierry, 

Can I get an Ack on this please? 

> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> ---
>  drivers/gpu/drm/tegra/dc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index b8403ed48285..49df2db2ad46 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -1359,7 +1359,7 @@ static u32 tegra_dc_get_vblank_counter(struct drm_crtc *crtc)
>  		return host1x_syncpt_read(dc->syncpt);
>  
>  	/* fallback to software emulated VBLANK counter */
> -	return drm_crtc_vblank_count(&dc->base);
> +	return (u32)drm_crtc_vblank_count(&dc->base);
>  }
>  
>  static int tegra_dc_enable_vblank(struct drm_crtc *crtc)
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