Re: [Intel-gfx] [PATCH 16/22] drm/tilcdc: Use drm_mode_copy()

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

On 18/02/2022 12:03, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> struct drm_display_mode embeds a list head, so overwriting
> the full struct with another one will corrupt the list
> (if the destination mode is on a list). Use drm_mode_copy()
> instead which explicitly preserves the list head of
> the destination mode.
> 
> Even if we know the destination mode is not on any list
> using drm_mode_copy() seems decent as it sets a good
> example. Bad examples of not using it might eventually
> get copied into code where preserving the list head
> actually matters.
> 
> Obviously one case not covered here is when the mode
> itself is embedded in a larger structure and the whole
> structure is copied. But if we are careful when copying
> into modes embedded in structures I think we can be a
> little more reassured that bogus list heads haven't been
> propagated in.
> 
> @is_mode_copy@
> @@
> drm_mode_copy(...)
> {
> ...
> }
> 
> @depends on !is_mode_copy@
> struct drm_display_mode *mode;
> expression E, S;
> @@
> (
> - *mode = E
> + drm_mode_copy(mode, &E)
> |
> - memcpy(mode, E, S)
> + drm_mode_copy(mode, E)
> )
> 
> @depends on !is_mode_copy@
> struct drm_display_mode mode;
> expression E;
> @@
> (
> - mode = E
> + drm_mode_copy(&mode, &E)
> |
> - memcpy(&mode, E, S)
> + drm_mode_copy(&mode, E)
> )
> 
> @@
> struct drm_display_mode *mode;
> @@
> - &*mode
> + mode
> 
> Cc: Jyri Sarha <jyri.sarha@iki.fi>
> Cc: Tomi Valkeinen <tomba@kernel.org>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>   drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> index 29890d704cb4..853c6b443fff 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> @@ -433,7 +433,7 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc)
>   
>   	set_scanout(crtc, fb);
>   
> -	crtc->hwmode = crtc->state->adjusted_mode;
> +	drm_mode_copy(&crtc->hwmode, &crtc->state->adjusted_mode);
>   
>   	tilcdc_crtc->hvtotal_us =
>   		tilcdc_mode_hvtotal(&crtc->hwmode);

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

  Tomi