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 A0ED9C433EF for ; Mon, 21 Mar 2022 18:05:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351893AbiCUSGb (ORCPT ); Mon, 21 Mar 2022 14:06:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60460 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241367AbiCUSG3 (ORCPT ); Mon, 21 Mar 2022 14:06:29 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1FDE5DE4C for ; Mon, 21 Mar 2022 11:05:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=+zScwtX/0ywSew6B96Ie7Los4HXBqMBl4omHP7aKR20=; b=Yxg3Sck22bJIBXWdYeu1MSghNA eu5QpotV/MH5f/7hKrBXUJpIGTxiLClWOW9VbqKPXP2L9QcGgdHCiF6KX3Q9Ltl/IlLBix6kVj2Do ddaveWLy3aBJpacLKlA7vRbjH8rt2YsMNO0bpSwmiRHhJeIz/T3BcR5887S324WZ5E7Hzg1ASiSFc 3w3yhIBZ1bSMWlxCWeLrlFPU88AUSlPeu0NS9SWuQtZhcO4OvHffO/KMkRCPSvTZ59lZ5OVe1wnWv QjYBCKikz8IffhdI0vnPzYD7R2rkcwDpVPTLQ8cUS+O2pfKQ/82Y9A1GbP21FRDC/B+C2bI6m6Qlp kFJyhmBw==; Received: from [187.39.124.208] (helo=[192.168.0.110]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1nWMOn-0008Ht-Mr; Mon, 21 Mar 2022 19:04:58 +0100 Message-ID: <307799df-fddd-6c46-7dd5-323ea5628892@igalia.com> Date: Mon, 21 Mar 2022 15:04:34 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: Question about the Broadcom Always On register panic handling Content-Language: en-US To: Florian Fainelli , computersforpeace@gmail.com Cc: "Guilherme G. Piccoli" , opendmb@gmail.com, justinpopo6@gmail.com, mmayer@broadcom.com, bcm-kernel-feedback-list@broadcom.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <6dac422b-d509-b863-0b31-98a07808ac0d@igalia.com> <781cafb0-8d06-8b56-907a-5175c2da196a@gmail.com> From: "Guilherme G. Piccoli" In-Reply-To: <781cafb0-8d06-8b56-907a-5175c2da196a@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/03/2022 13:32, Florian Fainelli wrote: > [...] > The AON (standing for always-on) is a small domain in the SoC that can > retain its state across various system wide sleep states and specific > reset conditions. The AON DATA RAM is a small ram of a few words (< 1KB) > which can store persistent information across such events. > > The purpose of this write was initially to help with indicating to the > boot loader that a panic occurred and so that it should try its best to > preserve the DRAM contents holding that buffer for recovery by the Linux > kernel as opposed to wiping out DRAM clean again. I cannot go into the > mechanics of what happens publicly unfortunately. > Thanks a lot Florian! This is very good information, it's enough for me - I'd like to be sure it's not rebooting the board or something "extreme" like that, so in the end...it's kinda the opposite, it's preserving the DRAM. >> >> Any information that helps me to document such panic event is very >> welcome, and in case you have AON documentation, it'd be also pretty great! > > Why are you asking specifically about this if I may ask? If you are a > legitimate Broadcom STB customer you can reach out to our support and I > am sure the question will come back for me to answer. Oh I'm not a Broadcom STB customer, I'm just working in the panic notifiers and was curious about this one. When I submit my series (soon) it's likely that there will be a small refactor of this notifier plus a comment, with your great explanation. Regarding the full AON documentation, I just asked in case it's public and I couldn't find - it's unfortunate that a lot of code in the kernel is based on closed specifications, but I understand we can't do much about that. Your response was very useful, and enough for my work =) Cheers, Guilherme