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[209.51.188.17]) by mx.google.com with ESMTPS id o20-20020a05622a009400b0031eb390dd83si589717qtw.376.2022.07.28.07.53.53 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Thu, 28 Jul 2022 07:53:54 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=JnaGl0W7; spf=pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from localhost ([::1]:42842 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oH4td-0008Rs-K3 for alex.bennee@linaro.org; Thu, 28 Jul 2022 10:53:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55122) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oH4q9-0006MU-6e for qemu-devel@nongnu.org; Thu, 28 Jul 2022 10:50:17 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:41748) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oH4q5-0005Ll-Gw for qemu-devel@nongnu.org; Thu, 28 Jul 2022 10:50:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659019812; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=h1THK366nG+yLMgHoIdTGT8kQ1oG9u1RyeAzzR/3KV8=; b=JnaGl0W77Xfn0LP5VK6E2yd87V0IetMsLwLDajjLYEkzFjzod0vchWfiowKJ2pL/67mAJr wcADW9w+uJTr24+Zekb5GVS/yJaLuRAVZuy2+EdWmYuv1JDjqxNQC+yqxCf9rxtKOW34hx 2T43Bzwy0j4s5k7aVaj01rvTZorNTFg= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-185-Gy4yZ42fOnivYoaQEuBBTw-1; Thu, 28 Jul 2022 10:50:08 -0400 X-MC-Unique: Gy4yZ42fOnivYoaQEuBBTw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id DA92218A6506; Thu, 28 Jul 2022 14:50:07 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.194.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 592B72166B26; Thu, 28 Jul 2022 14:50:07 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id EE2D421E6930; Thu, 28 Jul 2022 16:50:05 +0200 (CEST) From: Markus Armbruster To: Kevin Wolf Cc: Peter Maydell , Hao Wu , richard.henderson@linaro.org, qemu-arm@nongnu.org, qemu-devel@nongnu.org, venture@google.com, Avi.Fishman@nuvoton.com, kfting@nuvoton.com, hskinnemoen@google.com, f4bug@amsat.org, bin.meng@windriver.com, qemu-block@nongnu.org, thuth@redhat.com, Hanna Reitz Subject: Re: [PATCH v5 5/8] blockdev: Add a new IF type IF_OTHER References: <20220714182836.89602-1-wuhaotsh@google.com> <20220714182836.89602-6-wuhaotsh@google.com> <87ilnuda33.fsf@pond.sub.org> Date: Thu, 28 Jul 2022 16:50:05 +0200 In-Reply-To: (Kevin Wolf's message of "Thu, 28 Jul 2022 15:29:58 +0200") Message-ID: <878rodxpeq.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org Sender: "Qemu-devel" X-TUID: pX9KxuEWB8+W Kevin Wolf writes: > Am 28.07.2022 um 11:46 hat Peter Maydell geschrieben: >> On Wed, 27 Jul 2022 at 20:03, Kevin Wolf wrote: >> > >> > Am 18.07.2022 um 11:49 hat Markus Armbruster geschrieben: >> > > An OTP device isn't really a parallel flash, and neither are eFuses. >> > > More fast-and-lose use of IF_PFLASH may exist in the tree, and maybe of >> > > other interface types, too. >> > > >> > > This patch introduces IF_OTHER. The patch after next uses it for an >> > > EEPROM device. >> > > >> > > Do we want IF_OTHER? >> > >> > What would the semantics even be? Any block device that doesn't pick up >> > a different category may pick up IF_OTHER backends? >> > >> > It certainly feels like a strange interface to ask for "other" disk and >> > then getting as surprise what this other thing might be. It's >> > essentially the same as having an explicit '-device other', and I >> > suppose most people would find that strange. >> > >> > > If no, I guess we get to abuse IF_PFLASH some more. >> > > >> > > If yes, I guess we should use IF_PFLASH only for actual parallel flash >> > > memory going forward. Cleaning up existing abuse of IF_PFLASH may not >> > > be worth the trouble, though. >> > > >> > > Thoughts? >> > >> > If the existing types aren't good enough (I don't have an opinion on >> > whether IF_PFLASH is a good match), let's add a new one. But a specific >> > new one, not just "other". >> >> I think the common thread is "this isn't what anybody actually thinks >> of as being a 'disk', but we would like to back it with a block device >> anyway". That can cover a fair range of possibilities... > > How confident are we that no board will ever have two devices of this > kind? > > As long as every board has at most one, if=other is a bad user interface > in terms of descriptiveness, but still more or less workable as long as > you know what it means for the specific board you use. > > But if you have more than one device, it becomes hard to predict which > device gets which backend - it depends on the initialisation order in > the code then, Really? Board code should use IF_OTHER devices just like it uses the other interface types, namely connecting each frontend device to a backend device with a well-known and fixed interface type and index (or bus and unit instead, where appropriate). > and I'm pretty sure that this isn't something that should > have significance in external interfaces and therefore become a stable > API. I agree that "implied by execution order" is a bad idea: commit 95fd260f0a "blockdev: Drop unused drive_get_next()".