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Tue, 23 Dec 2025 02:48:43 -0800 (PST) X-Google-Smtp-Source: AGHT+IEGKGRq2ffp7hGOh+N5A3dzp/NoIb6jP9M8gUpRTD+0+rRLBvYqvrBUqBrw6Oxlq1LRAApRRw== X-Received: by 2002:a17:903:38c3:b0:269:82a5:f9e9 with SMTP id d9443c01a7336-2a2f2836764mr139760985ad.29.1766486923433; Tue, 23 Dec 2025 02:48:43 -0800 (PST) Received: from [10.217.217.147] ([202.46.22.19]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7ff7b22536esm13253932b3a.23.2025.12.23.02.48.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Dec 2025 02:48:43 -0800 (PST) Message-ID: Date: Tue, 23 Dec 2025 16:18:20 +0530 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] clk: qcom: rcg2: compute 2d using duty fraction directly To: Bjorn Andersson Cc: Michael Turquette , Stephen Boyd , Taniya Das , Ajit Pandey , Imran Shaik , Jagadeesh Kona , linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org References: <20251222-duty_cycle_precision-v1-1-b0da8e9fdab7@oss.qualcomm.com> Content-Language: en-US From: Taniya Das In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Authority-Analysis: v=2.4 cv=TOdIilla c=1 sm=1 tr=0 ts=694a738c cx=c_pps a=cmESyDAEBpBGqyK7t0alAg==:117 a=fChuTYTh2wq5r3m49p7fHw==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=COk6AnOGAAAA:8 a=EUspDBNiAAAA:8 a=MOVBJHszn32KNyIy_nMA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=1OuFwYUASf3TG4hYMiVC:22 a=TjNXssC_j7lpFel5tvFf:22 X-Proofpoint-ORIG-GUID: 9TF3GGadDx4jHxa6hlLiiBQ01OqIc2eL X-Proofpoint-GUID: 9TF3GGadDx4jHxa6hlLiiBQ01OqIc2eL X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjIzMDA4NiBTYWx0ZWRfX2jndVCDKPWCZ 5ugqiu/FtUmJrPNdaJs8D1VTIoxoxdhspicROpQUwZW6dbD0cU27+PE8908Cp0BnQUFrfP/imh5 qS8l0TM6Zu52W4bGXoBhZCyJ2gp1Gwfbch10/o8Jf4bsl+hMSPvho/7h1xBRVVxz5qzon8JSASp HlA2+xuF2UIFahYUoEpBeZFintA57MukDSdyxqLw4u5RzgXvn9puZsKc3sS5TqS0cMu3xMpP+Bg d47k7IOwK+gC7zHTug3xBjRhGuuL8X3tBt78fkufpjBm6pFi5HobJCQ/mV0XvsRKjdWM5JrRlDM ufQAVmJZiDXUdF2CD4karh8y/XpXNq7r+10rJLwp+76ueJ1t7Z4RicffFTMYg/A7lXBkaQ3nQFn ggOCJywtFYYlYAyI+lFIigkHvbeYf4qDCuvRvZbguDiRc8zixtNV3410gDpTnOF2l3/pBqWzfGA PF+CZZ+6J7m61y9P6/w== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-23_03,2025-12-22_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 priorityscore=1501 clxscore=1015 impostorscore=0 bulkscore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2512120000 definitions=main-2512230086 On 12/23/2025 12:39 AM, Bjorn Andersson wrote: > On Mon, Dec 22, 2025 at 10:38:14PM +0530, Taniya Das wrote: >> From: Taniya Das > > Please use oss.qualcomm.com. > My bad, will update it. >> >> The duty-cycle calculation in clk_rcg2_set_duty_cycle() currently >> derives an intermediate percentage `duty_per = (num * 100) / den` and >> then computes: >> >> d = DIV_ROUND_CLOSEST(n * duty_per * 2, 100); >> >> This introduces integer truncation at the percentage step (division by >> `den`) and a redundant scaling by 100, which can reduce precision for >> large `den` and skew the final rounding. >> >> Compute `2d` directly from the duty fraction to preserve precision and >> avoid the unnecessary scaling: >> >> d = DIV_ROUND_CLOSEST(n * duty->num * 2, duty->den); >> >> This keeps the intended formula `d ≈ n * 2 * (num/den)` while performing >> a single, final rounded division, improving accuracy especially for small >> duty cycles or large denominators. It also removes the unused `duty_per` >> variable, simplifying the code. >> >> There is no functional changes beyond improved numerical accuracy. >> >> Fixes: 7f891faf596ed ("clk: qcom: clk-rcg2: Add support for duty-cycle for RCG") >> Signed-off-by: Taniya Das >> --- >> Signed-off-by: Taniya Das >> --- >> drivers/clk/qcom/clk-rcg2.c | 6 ++---- >> 1 file changed, 2 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c >> index e18cb8807d73534c6437c08aeb524353a2eab06f..2838d4cb2d58ea1e351d6a5599045c72f4dc3801 100644 >> --- a/drivers/clk/qcom/clk-rcg2.c >> +++ b/drivers/clk/qcom/clk-rcg2.c >> @@ -755,7 +755,7 @@ static int clk_rcg2_get_duty_cycle(struct clk_hw *hw, struct clk_duty *duty) >> static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty) >> { >> struct clk_rcg2 *rcg = to_clk_rcg2(hw); >> - u32 notn_m, n, m, d, not2d, mask, duty_per, cfg; >> + u32 notn_m, n, m, d, not2d, mask, cfg; >> int ret; >> >> /* Duty-cycle cannot be modified for non-MND RCGs */ >> @@ -774,10 +774,8 @@ static int clk_rcg2_set_duty_cycle(struct clk_hw *hw, struct clk_duty *duty) >> >> n = (~(notn_m) + m) & mask; >> >> - duty_per = (duty->num * 100) / duty->den; >> - >> /* Calculate 2d value */ >> - d = DIV_ROUND_CLOSEST(n * duty_per * 2, 100); >> + d = DIV_ROUND_CLOSEST(n * duty->num * 2, duty->den); > > This looks better/cleaner. But for my understanding, can you share some > example numbers that shows the problem? > Sure Bjorn, will share the examples. > Regards, > Bjorn > >> >> /* >> * Check bit widths of 2d. If D is too big reduce duty cycle. >> >> --- >> base-commit: cc3aa43b44bdb43dfbac0fcb51c56594a11338a8 >> change-id: 20251222-duty_cycle_precision-796542baecab >> >> Best regards, >> -- >> Taniya Das >> -- Thanks, Taniya Das