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 5A4F9C433F5 for ; Fri, 8 Oct 2021 05:43:12 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 27867610CE for ; Fri, 8 Oct 2021 05:43:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 27867610CE Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=MXiH+31cw72l57rHz5X+L4ArO2YkYR/3CQ0CuPVd6KA=; b=MdNeqHABhOsZmT 4DA1idN409E+8vfxRxRoFilTSMUn2DehUSeyro2eJCb6bVbicCBPXSf0LcHf20x7wrOFJkxBTYEY3 rlGeN2EHUZsEh2S20I51rB5W8Tuy0kZfPLkgYv5jTvuX7hQPz+XfQ6EwijnKsaAyUZ0RNfZzavg6h AAlch2Z7CheGG8tfq7pXYN74V5u0LtecCPvFk5Zm35DBULIXFap3YGJf3s5QuyBj54Plbh7iQpOJ7 z4j/cp6mhsvk3GcHfQWYQdElbwKMkyPROhDQeADQ+YlRTuvs9aDuJebuRdvlXASHIyIh2NAWDXpWN n3j+vj0fSEFowWdt6AjA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mYid8-001dNN-G1; Fri, 08 Oct 2021 05:41:14 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mYid4-001dMa-KG for linux-arm-kernel@lists.infradead.org; Fri, 08 Oct 2021 05:41:12 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6EB27610D1; Fri, 8 Oct 2021 05:41:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1633671670; bh=u1tbswDt7HqRI5RWUKHZPssdcim/XVVZjEx5pIG+CMg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ksRQKgThzV3LCCTp5IHVcx639wObkNnoaf02iTL0mh/4560DVjusfOxwSGu2chU5d KnR9o7QfSZEhot2jH+D9Pa57VCxMr/+aI9PfucA1ODRM/KakFE3ivhPRmKGnmcrvut /STTZLv7h/MJMH4hGJKiW1cI2d/UBrVMgYHGDhN4= Date: Fri, 8 Oct 2021 07:41:06 +0200 From: Greg Kroah-Hartman To: Rob Herring Cc: Zev Weiss , Andy Shevchenko , OpenBMC Maillist , Jeremy Kerr , Joel Stanley , 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-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211007_224110_723989_7B401D00 X-CRM114-Status: GOOD ( 39.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 07, 2021 at 03:03:43PM -0500, Rob Herring wrote: > On Thu, Oct 7, 2021 at 10:41 AM Zev Weiss wrote: > > > > 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? > > TBC, it's 'just' the general purpose userspace interface to apply > overlays that's missing. > > I did suggest what's done here as overlays are kind of an overkill for > this usecase. Much easier to write to a sysfs file than write an > overlay, compile it with dtc, and provide it to the kernel all just to > enable a device. > > Perhaps this could also be supported in the driver model directly. > Given the "what about ACPI question", that is probably what should be > done unless the answer is we don't care. I think we'd just need a flag > to create devices, but not bind automatically. Or maybe abusing > driver_override can accomplish that. The driver model already allows devices to be bound/unbound from drivers, but no, it does not allow new devices to be "created" from userspace as that is a very bus-specific thing to have happen. If this is "just" a platform device, perhaps add that logic to the platform bus code? thanks, greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel