linux-kernel - [PATCH] media: staging/ipu7: avoid division by 64-bit value

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Message-Id: <20250709145710.102669-1-arnd@kernel.org>
Date: Wed,  9 Jul 2025 16:56:56 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Bingbu Cao <bingbu.cao@...el.com>,
	Hans Verkuil <hverkuil@...all.nl>
Cc: Arnd Bergmann <arnd@...db.de>,
	Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>,
	linux-media@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] media: staging/ipu7: avoid division by 64-bit value

From: Arnd Bergmann <arnd@...db.de>

On 32-bit targets, this causes a link failure:

x86_64-linux-ld: drivers/staging/media/ipu7/ipu7-isys-csi-phy.o: in function `ipu7_isys_phy_config':
ipu7-isys-csi-phy.c:(.text+0x1509): undefined reference to `__udivdi3'

Note that this does not divide a 64-bit number by a 32-bit one as usual,
but the other way round, which is something that the compiler should
really be able to figure out but does not (as of gcc-15).

A few lines higher, a similar division is done using the incorrect div_u64()
that truncates the 64-bit divisor to 32 bits.

Change both to use the safe but slow div64_u64() helper.

Fixes: a516d36bdc3d ("media: staging/ipu7: add IPU7 input system device driver")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/staging/media/ipu7/ipu7-isys-csi-phy.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/media/ipu7/ipu7-isys-csi-phy.c b/drivers/staging/media/ipu7/ipu7-isys-csi-phy.c
index 4407750c7f40..b8c5db7ae300 100644
--- a/drivers/staging/media/ipu7/ipu7-isys-csi-phy.c
+++ b/drivers/staging/media/ipu7/ipu7-isys-csi-phy.c
@@ -734,6 +734,7 @@ static void ipu7_isys_cphy_config(struct ipu7_isys *isys, u8 id, u8 lanes,
 	u16 reg;
 	u16 val;
 	u32 i;
+	u64 r64;
 	u32 r;
 
 	if (is_ipu7p5(isys->adev->isp->hw_ver))
@@ -806,8 +807,8 @@ static void ipu7_isys_cphy_config(struct ipu7_isys *isys, u8 id, u8 lanes,
 		dwc_phy_write_mask(isys, id, reg, 2, 0, 2);
 	}
 
-	deass_thresh = (u16)div_u64_rem(7 * 1000 * 6, mbps * 5U, &r) + 1;
-	if (r != 0)
+	deass_thresh = (u16)div64_u64_rem(7 * 1000 * 6, mbps * 5U, &r64) + 1;
+	if (r64 != 0)
 		deass_thresh++;
 
 	reg = CORE_DIG_RW_TRIO0_2;
@@ -815,8 +816,7 @@ static void ipu7_isys_cphy_config(struct ipu7_isys *isys, u8 id, u8 lanes,
 		dwc_phy_write_mask(isys, id, reg + 0x400 * i,
 				   deass_thresh, 0, 7);
 
-	delay_thresh =
-		((224U - (9U * 7U)) * 1000U) / (5U * mbps) - 7U;
+	delay_thresh = div64_u64((224U - (9U * 7U)) * 1000U, 5U * mbps) - 7u;
 
 	if (delay_thresh < 1)
 		delay_thresh = 1;
-- 
2.39.5