dim: allow tags in backmerges

Linus prefers that we backmerge a specific tag instead of a random
point in his branch. Allow that.

I guess it'd be nice to somehow figure out where a tag came from, but
git doesn't namespace tags. So that idea is out of the window
unfortunately.

v2: Unlazy and also update the docs.

v3: Make the check work from anywhere, we need to move the cd a bit
up (Dave).

Requested-by: Dave Airlie <airlied@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Tested-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

2 files changed, 7 insertions, 3 deletions

diff --git a/dim b/dim
index e477d043458b..5ca4646ff685 100755
--- a/dim
+++ b/dim
@@ -1010,11 +1010,14 @@ function dim_backmerge
 	branch=${1:?$usage}
 	upstream=${2:?$usage}
 
+	cd $DIM_PREFIX/drm-tip
+
 	if ! dim_list_upstreams | grep -q "^$upstream\$"; then
-		warn_or_fail "$upstream is not an upstream branch"
+		if ! git rev-parse --verify -q "refs/tags/$upstream" > /dev/null ; then
+			warn_or_fail "$upstream is neither an upstream branch nor a tag"
+		fi
 	fi
 
-	cd $DIM_PREFIX/drm-tip
 	tip_remote=$(repo_to_remote drm-tip)
 	git fetch -q $tip_remote || true
 
diff --git a/dim.rst b/dim.rst
index a99e40678a2f..ed784fe20913 100644
--- a/dim.rst
+++ b/dim.rst
@@ -335,7 +335,8 @@ backmerge *branch* *upstream*
 
 Backmerges *upstream* into *branch*, making a few sanity checks on the way. The
 *upstream* we backmerge should be the same as used for sending out pull requests
-using **pull-request**.
+using **pull-request**. Alternatively it can also be a tag, which if available
+should be preferred.
 
 update-next
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