linux-kernel - [PATCH v2 2/2] of: reserved_mem: Use stable allocation order

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Message-Id: <20230510-dt-resv-bottom-up-v2-2-aeb2afc8ac25@gerhold.net>
Date:   Wed, 14 Jun 2023 21:20:43 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        devicetree@...r.kernel.org, devicetree-spec@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Stephan Gerhold <stephan@...hold.net>
Subject: [PATCH v2 2/2] of: reserved_mem: Use stable allocation order

sort() in Linux is based on heapsort which is not a stable sort
algorithm - equal elements are being reordered. For reserved memory in
the device tree this happens mainly for dynamic allocations: They do not
have an address to sort with, so they are reordered somewhat randomly
when adding/removing other unrelated reserved memory nodes.

Functionally this is not a big problem, but it's confusing during
development when all the addresses change after adding unrelated
reserved memory nodes.

Make the order stable by sorting dynamic allocations according to
the node order in the device tree. Static allocations are not affected
by this because they are still sorted by their (fixed) address.

Signed-off-by: Stephan Gerhold <stephan@...hold.net>
---
 drivers/of/of_reserved_mem.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 7f892c3dcc63..7ec94cfcbddb 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -268,6 +268,11 @@ static int __init __rmem_cmp(const void *a, const void *b)
 	if (ra->size > rb->size)
 		return 1;

+	if (ra->fdt_node < rb->fdt_node)
+		return -1;
+	if (ra->fdt_node > rb->fdt_node)
+		return 1;
+
 	return 0;
 }

-- 
2.40.1