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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=MdlFVKzu; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6676F606A31C; Thu, 29 Oct 2026 11:03:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=MdlFVKzu Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F6951F01828; Thu, 29 Oct 2026 11:03:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793271784; bh=lqdjZkQwVXgTMSk1QocnJZhAE2sMU/4Mo4N5OcDK2FQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MdlFVKzuWxOxSjNjAhnFHwPZSKwPu5DlnspZZDlB0/cJmbVUI+7dUAXHJcsUW2pPb 3wLgn9zUorPGJNR4YgijvuBCkqfz0wmaR1NLHrTH+50fiHo9vx5iT1682o0qKET4J+ 5PLKVBtfJJnwdtRit0dsHNmfyBzPkvN/VPmirZM5R9NfuC8ppWwrYM5xQPuSEzu0l1 +xZhdpSEbo8k3dgPtmHi35AzoOXVtHjLAjruYIiQl/1fya5kQKNoIvPs5a2evjEHoV rv6b2t6D/WWkoxy7tA0MkFAFM4dJJUT54FMBICT5N3KKpMqy/1y1+GNCO0AjfVoDGU /lz+sftOX6tjQ== Message-ID: <8a675e45-eed1-406c-a503-e1490d10b638@kernel.org> Date: Thu, 29 Oct 2026 11:03:00 +0000 X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/14] media: qcom: camss: Introduce CPU latency QoS during streaming To: Loic Poulain , bryan.odonoghue@linaro.org Cc: Vladimir Zapolskiy , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261029-v4l2-frame-sync-v1-0-d37992559c58@kernel.org> <20261029-v4l2-frame-sync-v1-1-d37992559c58@kernel.org> From: Bryan O'Donoghue Content-Language: en-GB Autocrypt: addr=bod@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29/10/2026 10:10, Loic Poulain wrote: >> + >> +void camss_cpu_latency_get(struct camss *camss) >> +{ >> + mutex_lock(&camss->cpu_latency_lock); >> + >> + if (camss->cpu_latency_users++ == 0) >> + cpu_latency_qos_add_request(&camss->cpu_latency, >> + CAMSS_CPU_LATENCY_US); >> + >> + mutex_unlock(&camss->cpu_latency_lock); > I agree that we need such a latency request mechanism, but the current > approach requires additional logic and locking. > > What about one of the following alternatives instead? > - Move the latency request handling to the suspend/resume paths. The > request lifecycle would then be naturally serialized and balanced, and > in practice there are very few cases where the device is resumed but > not actively streaming. > - Alternatively, add a dedicated latency request instance to each VFE > and let each VFE manage its own request during start/stop. That would > keep the ownership local to the VFE and avoid the need for extra > locking altogether. > > Regards, > Loic yeah both of those would work. I'll have a think about that, thx --- bod