linux-kernel - [PATCH][next] mtd: rawnand: Replace one-element array with flexible-array member

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Message-ID: <20200930210824.GA12277@embeddedor>
Date:   Wed, 30 Sep 2020 16:08:24 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Stefan Agner <stefan@...er.ch>, Lucas Stach <dev@...xeye.de>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>
Cc:     linux-mtd@...ts.infradead.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] mtd: rawnand: Replace one-element array with
 flexible-array member

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member
instead of a one-element array. Also, make use of the struct_size()
helper to calculate the size of the allocation for _nand_. In order
to keep the code as maintainable as possible and to keep _cs_ as an
array, add a new macro CS_N to aid in the allocation size calculation,
in case there is a need for more Chip Select IDs in the future. In the
meantime, the macro is set to 1. This also avoids having to use a magic
number '1' as the last argument for struct_size().

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays

Build-tested-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/5f7473c0.Vv4h6yzXSga90P04%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/mtd/nand/raw/tegra_nand.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/raw/tegra_nand.c b/drivers/mtd/nand/raw/tegra_nand.c
index fbf67722a049..43b8359dcd85 100644
--- a/drivers/mtd/nand/raw/tegra_nand.c
+++ b/drivers/mtd/nand/raw/tegra_nand.c
@@ -163,6 +163,9 @@
 				HWSTATUS_RBSY_MASK(NAND_STATUS_READY) | \
 				HWSTATUS_RBSY_VALUE(NAND_STATUS_READY))
 
+/* Number of Chip Selects. Currently, only one. */
+#define CS_N			1
+
 struct tegra_nand_controller {
 	struct nand_controller controller;
 	struct device *dev;
@@ -183,7 +186,7 @@ struct tegra_nand_chip {
 	u32 config;
 	u32 config_ecc;
 	u32 bch_config;
-	int cs[1];
+	int cs[];
 };
 
 static inline struct tegra_nand_controller *
@@ -1086,14 +1089,14 @@ static int tegra_nand_chips_init(struct device *dev,
 		return -EINVAL;
 	}
 
-	/* Retrieve CS id, currently only single die NAND supported */
+	/* Retrieve CS id, currently only single-die NAND supported */
 	ret = of_property_read_u32(np_nand, "reg", &cs);
 	if (ret) {
 		dev_err(dev, "could not retrieve reg property: %d\n", ret);
 		return ret;
 	}
 
-	nand = devm_kzalloc(dev, sizeof(*nand), GFP_KERNEL);
+	nand = devm_kzalloc(dev, struct_size(nand, cs, CS_N), GFP_KERNEL);
 	if (!nand)
 		return -ENOMEM;
 
-- 
2.27.0