[PATCH][next] drm/i915/gem: Fix fall-through warning for Clang

[PATCH][next] drm/i915/gem: Fix fall-through warning for Clang

[Gustavo A. R. Silva]

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
warning by explicitly adding a fallthrough; statement.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
JFYI: We had thousands of these sorts of warnings and now we are down
      to just 13 in linux-next(20210607). This is one of those last
      remaining warnings. :)

 drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
index f4fb68e8955a..17714da24033 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
@@ -62,6 +62,7 @@ static void try_to_writeback(struct drm_i915_gem_object *obj,
 	switch (obj->mm.madv) {
 	case I915_MADV_DONTNEED:
 		i915_gem_object_truncate(obj);
+		fallthrough;
 	case __I915_MADV_PURGED:
 		return;
 	}
-- 
2.27.0

Re: [PATCH][next] drm/i915/gem: Fix fall-through warning for Clang

[Joe Perches]

On Mon, 2021-06-07 at 15:32 -0500, Gustavo A. R. Silva wrote:
> In preparation to enable -Wimplicit-fallthrough for Clang, fix a
> warning by explicitly adding a fallthrough; statement.
[]
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
[]
> @@ -62,6 +62,7 @@ static void try_to_writeback(struct drm_i915_gem_object *obj,
>  	switch (obj->mm.madv) {
>  	case I915_MADV_DONTNEED:
>  		i915_gem_object_truncate(obj);
> +		fallthrough;
>  	case __I915_MADV_PURGED:
>  		return;
>  	}

I think fallthrough to return is not particularly nice to follow.

This is the current function:

static void try_to_writeback(struct drm_i915_gem_object *obj,
			     unsigned int flags)
{
	switch (obj->mm.madv) {
	case I915_MADV_DONTNEED:
		i915_gem_object_truncate(obj);
	case __I915_MADV_PURGED:
		return;
	}

	if (flags & I915_SHRINK_WRITEBACK)
		i915_gem_object_writeback(obj);
}

One of these might be more typical:

static void try_to_writeback(struct drm_i915_gem_object *obj,
			     unsigned int flags)
{
	switch (obj->mm.madv) {
	case I915_MADV_DONTNEED:
		i915_gem_object_truncate(obj);
		break;
	case __I915_MADV_PURGED:
		break;
	default:
		if (flags & I915_SHRINK_WRITEBACK)
			i915_gem_object_writeback(obj);
		break;
	}
}

or maybe:

static void try_to_writeback(struct drm_i915_gem_object *obj,
			     unsigned int flags)
{
	switch (obj->mm.madv) {
	case I915_MADV_DONTNEED:
		i915_gem_object_truncate(obj);
		return;
	case __I915_MADV_PURGED:
		return;
	}

	if (flags & I915_SHRINK_WRITEBACK)
		i915_gem_object_writeback(obj);
}