Re: [PATCH 2/3] drm/i915/sdvo: Robustify the dtd<->drm_mode conversions

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 10, 2013 at 12:06:51PM +0200, Daniel Vetter wrote:
> We've failed to properly clear out the flags when converting a dtd to
> a drm mode. For more paranoia just memset the entire structure (and
> drop the now redundant clears).
> 
> Also since
> 
> commit 135c81b8c3c9a70d7b55758c9c2a247a4abb7b64
> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> Date:   Sun Jul 21 21:37:09 2013 +0200
> 
>     drm/i915: clean up crtc timings computation
> 
> we don't update the crtc timings any more properly, so do that again.
> 
> Cc: Rodrigo Vivi <rodrigo.vivi@gmail.com>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_sdvo.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
> index 5033c74..d4a046d 100644
> --- a/drivers/gpu/drm/i915/intel_sdvo.c
> +++ b/drivers/gpu/drm/i915/intel_sdvo.c
> @@ -788,6 +788,8 @@ static void intel_sdvo_get_dtd_from_mode(struct intel_sdvo_dtd *dtd,
>  	uint16_t h_sync_offset, v_sync_offset;
>  	int mode_clock;
>  
> +	memset(dtd, 0, sizeof(*dtd));
> +
>  	width = mode->hdisplay;
>  	height = mode->vdisplay;
>  
> @@ -830,14 +832,14 @@ static void intel_sdvo_get_dtd_from_mode(struct intel_sdvo_dtd *dtd,
>  	if (mode->flags & DRM_MODE_FLAG_PVSYNC)
>  		dtd->part2.dtd_flags |= DTD_FLAG_VSYNC_POSITIVE;
>  
> -	dtd->part2.sdvo_flags = 0;
>  	dtd->part2.v_sync_off_high = v_sync_offset & 0xc0;
> -	dtd->part2.reserved = 0;
>  }
>  
>  static void intel_sdvo_get_mode_from_dtd(struct drm_display_mode * mode,
>  					 const struct intel_sdvo_dtd *dtd)
>  {
> +	memset(mode, 0, sizeof(*mode));

I have a theoretical worry that someone might end up calling this on a
mode that sits on some list or was actually allocated and has a proper
object id which we'd leak here.

To make it totally safe you could populate a pristine mode struct and
use drm_mode_copy() to overwrite adjusted_mode. Assuming we're not so
short on stack space that our oversized mode struct would cause issues.
Other options would be to add some WARNs to catch wrongdoers, or embed
a temp mode for this purpose inside the intel_sdvo struct.

> +
>  	mode->hdisplay = dtd->part1.h_active;
>  	mode->hdisplay += ((dtd->part1.h_high >> 4) & 0x0f) << 8;
>  	mode->hsync_start = mode->hdisplay + dtd->part2.h_sync_off;
> @@ -872,6 +874,8 @@ static void intel_sdvo_get_mode_from_dtd(struct drm_display_mode * mode,

Somewhere around these parts we have:

'mode->flags &= ~(DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);'

It can now be eliminated.


>  		mode->flags |= DRM_MODE_FLAG_PVSYNC;
>  	else
>  		mode->flags |= DRM_MODE_FLAG_NVSYNC;
> +
> +	drm_mode_set_crtcinfo(mode);
>  }
>  
>  static bool intel_sdvo_check_supp_encode(struct intel_sdvo *intel_sdvo)
> -- 
> 1.8.4.rc3

-- 
Ville Syrjälä
Intel OTC