linux-kernel - Re: [PATCH] drm/i915: simplify switch to if-elseif

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Date:   Tue, 23 May 2023 16:26:29 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Tom Rix <trix@...hat.com>, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, tvrtko.ursulin@...ux.intel.com,
        airlied@...il.com, daniel@...ll.ch, nathan@...nel.org,
        ndesaulniers@...gle.com, ville.syrjala@...ux.intel.com,
        imre.deak@...el.com, arun.r.murthy@...el.com,
        lucas.demarchi@...el.com
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Tom Rix <trix@...hat.com>
Subject: Re: [PATCH] drm/i915: simplify switch to if-elseif

On Tue, 23 May 2023, Tom Rix <trix@...hat.com> wrote:
> clang with W=1 reports
> drivers/gpu/drm/i915/display/intel_display.c:6012:3: error: unannotated
>   fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
>                 case I915_FORMAT_MOD_X_TILED:
>                 ^
>
> Only one case and the default does anything in this switch, so it should
> be changed to an if-elseif.

Thanks for the patch.

If I wanted to fix this quickly, I'd just add the break in there.

If I wanted to fix this properly, I'd add a function
modifier_supports_async_flips() or something, and replace the switch
with:

	if (!modifier_supports_async_flips(i915, new_plane_state->hw.fb->modifier)) {
		drm_dbg_kms(&i915->drm, "[PLANE:%d:%s] Modifier does not support async flips\n",
			plane->base.base.id, plane->base.name);
		return -EINVAL;
	}

But I wouldn't just replace the switch with if-elseif. It doesn't help
with the overall feeling that intel_async_flip_check_hw() is too long.

BR,
Jani.


>
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 0490c6412ab5..1f852e49fc20 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5994,8 +5994,7 @@ static int intel_async_flip_check_hw(struct intel_atomic_state *state, struct in
>  		 * Need to verify this for all gen9 platforms to enable
>  		 * this selectively if required.
>  		 */
> -		switch (new_plane_state->hw.fb->modifier) {
> -		case DRM_FORMAT_MOD_LINEAR:
> +		if (new_plane_state->hw.fb->modifier == DRM_FORMAT_MOD_LINEAR) {
>  			/*
>  			 * FIXME: Async on Linear buffer is supported on ICL as
>  			 * but with additional alignment and fbc restrictions
> @@ -6008,13 +6007,10 @@ static int intel_async_flip_check_hw(struct intel_atomic_state *state, struct in
>  					    plane->base.base.id, plane->base.name);
>  				return -EINVAL;
>  			}
> -
> -		case I915_FORMAT_MOD_X_TILED:
> -		case I915_FORMAT_MOD_Y_TILED:
> -		case I915_FORMAT_MOD_Yf_TILED:
> -		case I915_FORMAT_MOD_4_TILED:
> -			break;
> -		default:
> +		} else if (!(new_plane_state->hw.fb->modifier == I915_FORMAT_MOD_X_TILED ||
> +			     new_plane_state->hw.fb->modifier == I915_FORMAT_MOD_Y_TILED ||
> +			     new_plane_state->hw.fb->modifier == I915_FORMAT_MOD_Yf_TILED ||
> +			     new_plane_state->hw.fb->modifier == I915_FORMAT_MOD_4_TILED)) {
>  			drm_dbg_kms(&i915->drm,
>  				    "[PLANE:%d:%s] Modifier does not support async flips\n",
>  				    plane->base.base.id, plane->base.name);

-- 
Jani Nikula, Intel Open Source Graphics Center