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Wed, 03 Dec 2025 23:14:24 -0800 (PST) X-Google-Smtp-Source: AGHT+IGMj8ey2LgMUls5vb/bDVMguHBOIr4pbhmoevWwLaJZ3BPPsbZLE6wlw8i1niGvDyiNmkNTEQ== X-Received: by 2002:a17:90b:534e:b0:32b:9750:10e4 with SMTP id 98e67ed59e1d1-349126f0736mr5893429a91.27.1764832463957; Wed, 03 Dec 2025 23:14:23 -0800 (PST) Received: from [10.217.217.147] ([202.46.22.19]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3494f398fa5sm889313a91.8.2025.12.03.23.14.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Dec 2025 23:14:23 -0800 (PST) Message-ID: <75e53a37-0fd2-41d6-92bc-fb4ad5856829@oss.qualcomm.com> Date: Thu, 4 Dec 2025 12:44:16 +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 v2 08/11] clk: qcom: dispcc: Add support for display clock controller Kaanapali To: Konrad Dybcio , Dmitry Baryshkov Cc: Bjorn Andersson , Michael Turquette , Stephen Boyd , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Neil Armstrong , Maxime Coquelin , Alexandre Torgue , Vladimir Zapolskiy , Konrad Dybcio , Ajit Pandey , Imran Shaik , Jagadeesh Kona , linux-arm-msm@vger.kernel.org, linux-clk@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org References: <20251125-kaanapali-mmcc-v2-v2-0-fb44e78f300b@oss.qualcomm.com> <20251125-kaanapali-mmcc-v2-v2-8-fb44e78f300b@oss.qualcomm.com> <8d0ec7fc-6eb0-4b71-8e0f-3deaf1f489d6@oss.qualcomm.com> Content-Language: en-US From: Taniya Das In-Reply-To: <8d0ec7fc-6eb0-4b71-8e0f-3deaf1f489d6@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjA0MDA1NyBTYWx0ZWRfX8J9ykxrQpHm6 UqU/tjkxyPtE6bS0FtqDzWpVs0ETpqFX2S533XNmvX4fc2d7X45NM9dvQzh99F9R9Oq2IsbPjVg OYBIjzjskln6gtw+sLqnBZ2DPBoHuj8eZiqUiE5jAj1emVBbI2o7paF3wK8ZdGtBGPKqunhIw+A Dwk5M7wxsRUASd253D14146QdHzoCaUlw4HVef0yUkluP1tfYKR9yx9a2LW+zS7Fz/469c65GKV Hf6U4YxcoZm7daGJZPm7tcSgpvu0CeR2lYg4KoJq438NMd9n5i92WoN5trj8Du529M8JEPIrfaY VQNAzqTgAlcBdQY74YrfKQVy0EXV5vmibruDcvwKPEmtismuFo5TvNVnRvVFUB+9KygUBv68A2m pzfl1JtCYvhE30yEAuavoakHTpMwEw== X-Authority-Analysis: v=2.4 cv=JY6xbEKV c=1 sm=1 tr=0 ts=693134d1 cx=c_pps a=0uOsjrqzRL749jD1oC5vDA==:117 a=fChuTYTh2wq5r3m49p7fHw==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=EUspDBNiAAAA:8 a=JxPSEc7MvJ4Lh0wbHXUA:9 a=QEXdDO2ut3YA:10 a=mQ_c8vxmzFEMiUWkPHU9:22 X-Proofpoint-GUID: UELdEgAKxk4PzRfCLm2f2vVHWRihwHIO X-Proofpoint-ORIG-GUID: UELdEgAKxk4PzRfCLm2f2vVHWRihwHIO 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=2025-12-04_02,2025-12-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 adultscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 lowpriorityscore=0 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2512040057 On 12/1/2025 6:50 PM, Konrad Dybcio wrote: > On 11/26/25 1:09 AM, Dmitry Baryshkov wrote: >> On Tue, Nov 25, 2025 at 11:15:17PM +0530, Taniya Das wrote: >>> Support the clock controller driver for Kaanapali to enable display SW to >>> be able to control the clocks. >>> >>> Signed-off-by: Taniya Das >>> --- > > [...] > >>> +/* 257.142858 MHz Configuration */ >> >> This is a bit strange frequency for the boot config. The lowest PLL configuration is used as boot config based on the MDP_CLK_SRC clock requirement. The PLLs on Kaanapali can support these lower frequencies as well. > The frequency map lists this odd cookie as the lowest predefined config, > perhaps it was pulled from there. > Correct Konrad. > More interestingly, the only consumer of this PLL (MDP_CLK_SRC) makes no > effort to use the m/n/d registers, instead relying on the PLL to re-clock > for its ratesetting with a fixed divider of 3 (and div1 @ XO rate). > The m/n is not preferred in the cases where the PLL needs to slew to derive a new VCO frequency. That is the reason to keep the divider constant as much as possible to derive a particular frequency. > 257.142858 * 3 = 771.428574 over-drives MDP_CLK_SRC, FWIW. > The lowest frequency requirement is 85.7MHz and the frequency is derived using 257.142858 (PLL VCO) / 3 (RCG Div) = 85.714286 MHz there is no over-drive at RCG of MDP. > Taniya, we've seen something like this in camera too. Is there a reason > the frequency is being set this way? > We start with the lowest frequency to configure the PLL and frequency requirements are decided based on usecases. -- Thanks, Taniya Das