[PATCH] spi: spacemit: avoid 32-bit integer overflow warning

From: Arnd Bergmann <arnd@kernel.org>
To: Mark Brown <broonie@kernel.org>, Yixun Lan <dlan@kernel.org>,
	Alex Elder <elder@riscstar.com>,
	Guodong Xu <guodong@riscstar.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	linux-spi@vger.kernel.org, linux-riscv@lists.infradead.org,
	spacemit@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: [PATCH] spi: spacemit: avoid 32-bit integer overflow warning
Date: Tue,  5 May 2026 19:57:33 +0200	[thread overview]
Message-ID: <20260505175744.900750-1-arnd@kernel.org> (raw)

From: Arnd Bergmann <arnd@arndb.de>

Calculating the bit rate in nanoseconds does not fit into a 32-bit 'int'
type, as gcc-16 points out:

drivers/spi/spi-spacemit-k1.c: In function 'k1_spi_set_speed':
drivers/spi/spi-spacemit-k1.c:393:38: error: integer overflow in expression of type 'long int' results in '-589934592' [-Werror=overflow]
  393 |         nsec_per_word = NSEC_PER_SEC * BITS_PER_BYTE * drv_data->bytes;

Cast the value to a 64-bit constant to force the longer type for the
calculation.

Fixes: efcd8b9d1111 ("spi: spacemit: introduce SpacemiT K1 SPI controller driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
----
There is probably a way to rework the algorithm to avoid both the 64-bit
multiplication and the following division, but I kept this as a minimal
change.
---
 drivers/spi/spi-spacemit-k1.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-spacemit-k1.c b/drivers/spi/spi-spacemit-k1.c
index 99db429db0b2..215fe66d27b4 100644
--- a/drivers/spi/spi-spacemit-k1.c
+++ b/drivers/spi/spi-spacemit-k1.c
@@ -390,7 +390,7 @@ static int k1_spi_set_speed(struct k1_spi_driver_data *drv_data,
 	 *   ticks_per_word = BITS_PER_BYTE * drv_data->bytes;
 	 * We do the divide last for better accuracy.
 	 */
-	nsec_per_word = NSEC_PER_SEC * BITS_PER_BYTE * drv_data->bytes;
+	nsec_per_word = (u64)NSEC_PER_SEC * BITS_PER_BYTE * drv_data->bytes;
 	nsec_per_word = DIV_ROUND_UP_ULL(nsec_per_word, drv_data->rate);
 
 	/*
-- 
2.39.5


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