Re: [Intel-gfx] [PATCH 19/22] drm/i915: Use drm_mode_copy()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 18 Feb 2022, Ville Syrjala <ville.syrjala@linux.intel.com> 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
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 74c5a99ab276..661e36435793 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5506,8 +5506,10 @@ intel_crtc_copy_uapi_to_hw_state_modeset(struct intel_atomic_state *state,
>  
>  	crtc_state->hw.enable = crtc_state->uapi.enable;
>  	crtc_state->hw.active = crtc_state->uapi.active;
> -	crtc_state->hw.mode = crtc_state->uapi.mode;
> -	crtc_state->hw.adjusted_mode = crtc_state->uapi.adjusted_mode;
> +	drm_mode_copy(&crtc_state->hw.mode,
> +		      &crtc_state->uapi.mode);
> +	drm_mode_copy(&crtc_state->hw.adjusted_mode,
> +		      &crtc_state->uapi.adjusted_mode);
>  	crtc_state->hw.scaling_filter = crtc_state->uapi.scaling_filter;
>  
>  	intel_crtc_copy_uapi_to_hw_state_nomodeset(state, crtc);
> @@ -5584,9 +5586,12 @@ copy_bigjoiner_crtc_state_modeset(struct intel_atomic_state *state,
>  	memset(&slave_crtc_state->hw, 0, sizeof(slave_crtc_state->hw));
>  	slave_crtc_state->hw.enable = master_crtc_state->hw.enable;
>  	slave_crtc_state->hw.active = master_crtc_state->hw.active;
> -	slave_crtc_state->hw.mode = master_crtc_state->hw.mode;
> -	slave_crtc_state->hw.pipe_mode = master_crtc_state->hw.pipe_mode;
> -	slave_crtc_state->hw.adjusted_mode = master_crtc_state->hw.adjusted_mode;
> +	drm_mode_copy(&slave_crtc_state->hw.mode,
> +		      &master_crtc_state->hw.mode);
> +	drm_mode_copy(&slave_crtc_state->hw.pipe_mode,
> +		      &master_crtc_state->hw.pipe_mode);
> +	drm_mode_copy(&slave_crtc_state->hw.adjusted_mode,
> +		      &master_crtc_state->hw.adjusted_mode);
>  	slave_crtc_state->hw.scaling_filter = master_crtc_state->hw.scaling_filter;
>  
>  	copy_bigjoiner_crtc_state_nomodeset(state, slave_crtc);

-- 
Jani Nikula, Intel Open Source Graphics Center