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[92.21.58.28]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454d612429csm73543555e9.23.2025.07.11.01.23.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Jul 2025 01:23:48 -0700 (PDT) Date: Fri, 11 Jul 2025 09:23:29 +0100 From: David Laight To: Arnd Bergmann Cc: Sakari Ailus , Mauro Carvalho Chehab , Greg Kroah-Hartman , Bingbu Cao , Hans Verkuil , Arnd Bergmann , Stanislaw Gruszka , linux-media@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] media: staging/ipu7: avoid division by 64-bit value Message-ID: <20250711092329.74e52573@pumpkin> In-Reply-To: <20250709145710.102669-1-arnd@kernel.org> References: <20250709145710.102669-1-arnd@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 9 Jul 2025 16:56:56 +0200 Arnd Bergmann wrote: > From: Arnd Bergmann > > 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 > --- > 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++; While 'mbps' is presumably u64, it can't be big. So this can just be: deass_threas = roundup(7 * 1000 * 6 / 5, (u32)mbps) + 1; > > 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; That one just needs a (u32) cast, although the 5 can be moved. David > > if (delay_thresh < 1) > delay_thresh = 1;