From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25C75C76195 for ; Mon, 27 Mar 2023 08:09:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232937AbjC0IJl (ORCPT ); Mon, 27 Mar 2023 04:09:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231946AbjC0IJk (ORCPT ); Mon, 27 Mar 2023 04:09:40 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 93893191; Mon, 27 Mar 2023 01:09:39 -0700 (PDT) Received: from [192.168.1.100] (2-237-20-237.ip236.fastwebnet.it [2.237.20.237]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: kholk11) by madras.collabora.co.uk (Postfix) with ESMTPSA id 97DDF6602087; Mon, 27 Mar 2023 09:09:37 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1679904578; bh=WsJrZpm843H/Mqkak9eNmuxfS+fyJ9GgkzGPM1UBOFY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MRMri0dpMSRlcR433ByuMgdZmR0JajiPP6xsngGy/nxPO5KOcUB0byRvbzhLRc99D hL41kgsF36sAAaLuskGkuY/mWTqL+4k1loJa50QP3npbNq0jz5511R7YZ9Rb7aFbXZ YDHQU1or1V1O1Q1DMy2kTyLxcMsZl7vxTO9pgU9M5bf7rNTqjmCIqtg+EhpWE2foSl 3J+Ujz2CKp4vZBT8LOlLcj943u7W2t10QfP52tDmNx46C69Pq6WcfpdXTqaXFosJu5 svMP6/z9mrvJ+E+izWpN5pIt92RpnRTEd1+Oat5V0P42zHO8Z5OpDw/gbTi+R8bM5p F3su3t1xiwMSg== Message-ID: <8937b354-a808-5e4b-94c4-f2c8a63945e2@collabora.com> Date: Mon, 27 Mar 2023 10:09:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v1 03/18] arm64: dts: mediatek: mt6795: xperia-m5: Enable Frequency Hopping Content-Language: en-US To: Pavel Machek Cc: matthias.bgg@gmail.com, qii.wang@mediatek.com, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org, jassisinghbrar@gmail.com, houlong.wei@mediatek.com, linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, kernel@collabora.com, phone-devel@vger.kernel.org, ~postmarketos/upstreaming@lists.sr.ht References: <20230324175456.219954-1-angelogioacchino.delregno@collabora.com> <20230324175456.219954-4-angelogioacchino.delregno@collabora.com> From: AngeloGioacchino Del Regno In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org Il 25/03/23 22:11, Pavel Machek ha scritto: > On Fri 2023-03-24 18:54:41, AngeloGioacchino Del Regno wrote: >> Enable FHCTL with Spread Spectrum for MAINPLL, MPLL and MSDCPLL >> as found on the downstream kernel for this smartphone. >> Which one to enable, and at what SSC percentage, was found by >> dumping the debugging data from a running downstream kernel and >> checking the downstream code. > > What advantages does this have? Lower EMI emissions? > Hello Pavel, this is done for multiple reasons, main one being lower EMI, but the effects on functionality, depending on the actual board, may be quite dramatic and ranging from lower WiFi and/or modem signal "sensitivity" (as in, for example, having to automatically lower signal gain because of signal disturbance from the conducted EMI ripple), to even a complete platform crash due to clocking issues. This is not about accounting for hardware quirks because having this situation is totally normal and expected, especially on "particular" usecases such as smartphones, where the actual board is typically much constrained in terms of space, and where on the same board you have multiple components generating noise, either wanted (a nfc/wifi/bt/2g/3g/4g/5g/something-else signal), or unwanted. Cheers! Angelo