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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51828C35247 for ; Mon, 3 Feb 2020 19:10:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 292A92082E for ; Mon, 3 Feb 2020 19:10:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726369AbgBCTKZ (ORCPT ); Mon, 3 Feb 2020 14:10:25 -0500 Received: from mx2.suse.de ([195.135.220.15]:47770 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726287AbgBCTKZ (ORCPT ); Mon, 3 Feb 2020 14:10:25 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 056FFB061; Mon, 3 Feb 2020 19:10:23 +0000 (UTC) Message-ID: Subject: Re: [PATCH] serial: 8250_early: Add earlycon for BCM2835 aux uart From: Nicolas Saenz Julienne To: Lukas Wunner Cc: Matthias Brugger , matthias.bgg@kernel.org, linux-arm-kernel@lists.infradead.org, Matthias Brugger , Scott Branden , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, Ray Jui , Stephen Boyd , Florian Fainelli , bcm-kernel-feedback-list@broadcom.com, linux-rpi-kernel@lists.infradead.org, linux-serial@vger.kernel.org, jslaby@suse.com Date: Mon, 03 Feb 2020 20:10:21 +0100 In-Reply-To: <20200131152414.73tgwsfhzgu4apkx@wunner.de> References: <20200128141958.vwbxoqglt5gw4xj5@wunner.de> <20200131152414.73tgwsfhzgu4apkx@wunner.de> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-rxZ/SqVaphyyjrFeqQty" User-Agent: Evolution 3.34.3 MIME-Version: 1.0 Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org --=-rxZ/SqVaphyyjrFeqQty Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2020-01-31 at 16:24 +0100, Lukas Wunner wrote: > On Thu, Jan 30, 2020 at 05:11:55PM +0100, Nicolas Saenz Julienne wrote: > > BTW did you had the oportunity to have a go at the patch? >=20 > I've just performed a quick test and it doesn't work for me. > If I add stdout-path =3D "serial1:115200n8"; to the chosen node, > I only get a regular console with this patch, not an earlycon. That's surprising, you're using u-boot isn't it? and the upstream device tr= ee? > > > The problem is that in mainline, bcm2835_defconfig contains: > > > CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE=3Dy > > >=20 > > > Likewise in the Foundation's downstream tree, bcmrpi_defconfig as wel= l > > > as bcm2711_defconfig and bcm2709_defconfig contain: > > > CONFIG_CPU_FREQ_DEFAULT_GOV_POWERSAVE=3Dy > > >=20 > > > In contrast to this, we set the following on Revolution Pi devices: > > > CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=3Dy > > >=20 > > > Downclocking influences not only the uart1 baud rate but also the > > > spi0 clock. We attach Ethernet chips to spi0, throughput was > > > significantly worse with the ondemand governor (which is what we > > > used previously). We felt that maximum Ethernet performance > > > outweighs the relatively small powersaving gains. > >=20 > > In that regard I suggest you use the upstream cpufreq driver which > > behaves properly in that regard. It disables GPU freq scaling, so as to > > change CPU frequencies without SPI/I2C/UART issues. >=20 > Okay, I'll take a look. But the uart1 baudrate will still be wrong > if the firmware downclocks because of overheating, right? You're right, it might happen. The way I understand it you're bound to leav= e the GPU at it's lower frequency if you want to use those peripherals and fo= r them to be reliable. You could technically try to empirically fine tune the= CPU thermal trip point so as to make sure the upstream kernel cpufreq downclock always kicks in before videocore's one. I'd actually like to see someone tr= y that. However short of using an RT kernel It think you'll never be 100% sur= e it can never happen. Regards, Nicolas --=-rxZ/SqVaphyyjrFeqQty Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl44cB0ACgkQlfZmHno8 x/4OKwf+KvsKB8pRgfFS6tQGkcjn5+7rl7qXYEndk80sawqCUn4/ZHkxPdoqD5cO bU8iTyaNfFQQb9uq8RoWcJrFMKQJhxGe8sjDNkZNqvbTUr3oM8ltCrjVWX7D5wfG eDSxB7hZqwE+BkdJaK3G5kicCfPl21opnQwZUn7R/0e0bYIuzMu/hq1xk7XiRaLU hL30AwUY3DLZtOVEeNIeVW9TVuVdnbu219TXZjtwuD+iZ9u2xbkh83fne8s0nW7O 79/Gejgu/e5PDH3CTnbheLNpl9Fws8fGiERnwXNbAD2XSj2kOfTitCVVNK2Efup5 txMswkwfPEC1JsGHkHgANzz5Z5UOVQ== =AW10 -----END PGP SIGNATURE----- --=-rxZ/SqVaphyyjrFeqQty--