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[78.88.45.245]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b9c3cff1c3dsm540062966b.49.2026.04.07.03.53.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Apr 2026 03:53:02 -0700 (PDT) Message-ID: <6550e862-590d-4b34-a12d-da3a6b285c5e@oss.qualcomm.com> Date: Tue, 7 Apr 2026 12:52:59 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/5] clk: qcom: clk-rcg2: use 64-bit arithmetic in set_duty_cycle() To: Xilin Wu , Bjorn Andersson , Michael Turquette , Stephen Boyd , Dzmitry Sankouski , Taniya Das , Mike Turquette Cc: linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Stephen Boyd References: <20260406-clk-qcom-gpclk-fixes-v1-0-7a14fe64552d@radxa.com> <20260406-clk-qcom-gpclk-fixes-v1-2-7a14fe64552d@radxa.com> Content-Language: en-US From: Konrad Dybcio In-Reply-To: <20260406-clk-qcom-gpclk-fixes-v1-2-7a14fe64552d@radxa.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Authority-Analysis: v=2.4 cv=dO6WXuZb c=1 sm=1 tr=0 ts=69d4e210 cx=c_pps a=7E5Bxpl4vBhpaufnMqZlrw==:117 a=FpWmc02/iXfjRdCD7H54yg==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=ZpdpYltYx_vBUK5n70dp:22 a=ksxQWNrZAAAA:8 a=EUspDBNiAAAA:8 a=YQxt2tlkmv6-1s3Hh8wA:9 a=QEXdDO2ut3YA:10 a=pJ04lnu7RYOZP9TFuWaZ:22 a=l7WU34MJF0Z5EO9KEJC3:22 X-Proofpoint-GUID: KbQYsapnXMI0y-C0CJRybCIgAKqD--73 X-Proofpoint-ORIG-GUID: KbQYsapnXMI0y-C0CJRybCIgAKqD--73 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDA3MDEwMSBTYWx0ZWRfX2F8/D23YuXuC vGVc7rzx55L3hqGoUyphPOz4n5n6IdVoIYb2Xb0b3eukBEfTT5Upr79xPoFMfzPJj/J6BJ9FWRB Nl7BV6Eg13A+kmHqJQBcREWLMySb7BVQfJEUXL+GWIOBMFkkj22W5uvNvs7JJjuGg9XVLJimRsb 68P82DLaaieT+fJhTaH3WnT5u5zeh2n6+Lmz3M5zM1XNUf4TCWUp/6PCh0Y9fPnj2GFmvveBCOq lgxo1FAS0ZqxH4fRv2mXBT77ev+TIatCZEyobF2uSuK/KQTVo2dr2+FjdsPqvDU9beZacpEJ+4K 1qYW65ZjDxWAY6NnG5hOwDYahdSvgR1HbTz9XqAwCXYF/XjX7ublHdfnADzpn8D26u6svRkWPBA BKQMcGce7/qAxo6wOhh58cZJjq76V/o534fhH4os++qkHtgRoZeY7l+pQhVOiDszOJiXGC+vprM +9q99CG+m1+oZwbbZHg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-07_02,2026-04-07_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 suspectscore=0 phishscore=0 bulkscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604070101 On 4/6/26 5:54 PM, Xilin Wu wrote: > The duty cycle calculation in clk_rcg2_set_duty_cycle() computes > "n * duty->num * 2" using u32 arithmetic. When n is large and > duty->num is also large, the intermediate result overflows u32. > > For example, requesting 50% duty on a 1 kHz output derived from a > 19.2 MHz parent gives n=19200, duty->num=500000, duty->den=1000000: > > 19200 * 500000 * 2 = 19,200,000,000 > U32_MAX (4,294,967,295) > > The truncated result produces a completely wrong duty cycle (5.26% > instead of the requested 50%). > > Use DIV_ROUND_CLOSEST_ULL() with an explicit (u64) cast to prevent > the overflow. > > Fixes: 7f891faf596e ("clk: qcom: clk-rcg2: Add support for duty-cycle for RCG") > Signed-off-by: Xilin Wu > --- I hate that we're still hitting this class of bugs in 2026 > drivers/clk/qcom/clk-rcg2.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c > index 82ee7ca1703a..0e8f0473897e 100644 > --- a/drivers/clk/qcom/clk-rcg2.c > +++ b/drivers/clk/qcom/clk-rcg2.c > @@ -783,7 +783,7 @@ static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty) > n = (~(notn_m) + m) & mask; > > /* Calculate 2d value */ > - d = DIV_ROUND_CLOSEST(n * duty->num * 2, duty->den); > + d = DIV_ROUND_CLOSEST_ULL((u64)n * duty->num * 2, duty->den); This may look scary given we feed it back into a u32 again, but given the CCF has a check that ensures 0 < duty <= 100% and I think n is generally < 16b wide, this should indeed never overflow Reviewed-by: Konrad Dybcio Konrad