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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61F1DC433EF for ; Thu, 7 Oct 2021 15:41:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C70160FC3 for ; Thu, 7 Oct 2021 15:41:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242387AbhJGPnO (ORCPT ); Thu, 7 Oct 2021 11:43:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234337AbhJGPnN (ORCPT ); Thu, 7 Oct 2021 11:43:13 -0400 Received: from thorn.bewilderbeest.net (thorn.bewilderbeest.net [IPv6:2605:2700:0:5::4713:9cab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58644C061570; Thu, 7 Oct 2021 08:41:19 -0700 (PDT) Received: from hatter.bewilderbeest.net (71-212-29-146.tukw.qwest.net [71.212.29.146]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: zev) by thorn.bewilderbeest.net (Postfix) with ESMTPSA id 5595F3F9; Thu, 7 Oct 2021 08:41:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bewilderbeest.net; s=thorn; t=1633621278; bh=Sp4De8iMtZ/6e2Np59FI+yTdsoee6zx033jfHJqL1Pc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=osSImv0naSv90iNaTrO7E06s7W++x6zvCTTPMROOgiTfywg5ODLiD6boZlkAh0jBO 18YZTarxBxjDUQESB9+wTQfy6L5oZsNKFCJbzgM+oiUnN4rG+5myF5vXMEijHzTa3t 9QLrBQncRbV0hoNa2Cqc/4rjtV5K6xRl0Uz4ksQU= Date: Thu, 7 Oct 2021 08:41:13 -0700 From: Zev Weiss To: Greg Kroah-Hartman Cc: Andy Shevchenko , OpenBMC Maillist , Jeremy Kerr , Joel Stanley , Rob Herring , devicetree , Andrew Jeffery , Frank Rowand , "Rafael J. Wysocki" , Andy Shevchenko , Andrew Morton , Francis Laniel , Kees Cook , Andrey Konovalov , Jonathan Cameron , Daniel Axtens , Alexey Dobriyan , Dan Williams , Daniel Vetter , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Heiner Kallweit , Nick Desaulniers , Linux Kernel Mailing List , linux-arm Mailing List , "moderated list:ARM/ASPEED MACHINE SUPPORT" Subject: Re: [PATCH 0/9] Dynamic DT device nodes Message-ID: References: <20211007000954.30621-1-zev@bewilderbeest.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 07, 2021 at 03:31:39AM PDT, Greg Kroah-Hartman wrote: >On Thu, Oct 07, 2021 at 02:05:41AM -0700, Zev Weiss wrote: >> On Thu, Oct 07, 2021 at 12:04:41AM PDT, Andy Shevchenko wrote: >> > On Thu, Oct 7, 2021 at 3:10 AM Zev Weiss wrote: >> > > This patch series is in some ways kind of a v2 for the "Dynamic >> > > aspeed-smc flash chips via 'reserved' DT status" series I posted >> > > previously [0], but takes a fairly different approach suggested by Rob >> > > Herring [1] and doesn't actually touch the aspeed-smc driver or >> > > anything in the MTD subsystem, so I haven't marked it as such. >> > > >> > > To recap a bit of the context from that series, in OpenBMC there's a >> > > need for certain devices (described by device-tree nodes) to be able >> > > to be attached and detached at runtime (for example the SPI flash for >> > > the host's firmware, which is shared between the BMC and the host but >> > > can only be accessed by one or the other at a time). >> > >> > This seems quite dangerous. Why do you need that? >> >> Sometimes the host needs access to the flash (it's the host's firmware, >> after all), sometimes the BMC needs access to it (e.g. to perform an >> out-of-band update to the host's firmware). To achieve the latter, the >> flash needs to be attached to the BMC, but that requires some careful >> coordination with the host to arbitrate which one actually has access to it >> (that coordination is handled by userspace, which then tells the kernel >> explicitly when the flash should be attached and detached). >> >> What seems dangerous? >> >> > Why can't device tree overlays be used? >> >> I'm hoping to stay closer to mainline. The OpenBMC kernel has a documented >> policy strongly encouraging upstream-first development: >> https://github.com/openbmc/docs/blob/master/kernel-development.md >> >> I doubt Joel (the OpenBMC kernel maintainer) would be eager to start >> carrying the DT overlay patches; I'd likewise strongly prefer to avoid >> carrying them myself as additional downstream patches. Hence the attempt at >> getting a solution to the problem upstream. > >Then why not work to get device tree overlays to be merged properly? >Don't work on a half-of-a-solution when the real solution is already >here. > I had been under the impression that the overlay patches had very dim prospects of ever being accepted and that this might be a more tractable alternative, but apparently was mistaken -- I'll look into what the outstanding issues were with that and perhaps take a stab at addressing them. Zev