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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6DA84C433F5 for ; Thu, 24 Feb 2022 11:48:20 +0000 (UTC) Received: from localhost ([::1]:60898 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nNCba-0005ig-01 for qemu-devel@archiver.kernel.org; Thu, 24 Feb 2022 06:48:18 -0500 Received: from eggs.gnu.org ([209.51.188.92]:36236) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nNCWt-0004Ll-JL for qemu-devel@nongnu.org; Thu, 24 Feb 2022 06:43:27 -0500 Received: from beetle.greensocs.com ([5.135.226.135]:60214) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nNCWq-0005uJ-IS for qemu-devel@nongnu.org; Thu, 24 Feb 2022 06:43:27 -0500 Received: from [192.168.13.13] (unknown [195.68.53.70]) by beetle.greensocs.com (Postfix) with ESMTPSA id 4272C20770; Thu, 24 Feb 2022 11:43:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=greensocs.com; s=mail; t=1645703002; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=suRoupgWcDoJhffVuDpcgIR5QwSobNDw/NzbEWPsjcQ=; b=T6az+wh5faQ1GCcRsUO2Q2sMq8JxRQ1Ql9SAaw2SThB5Xe+R4AAUBy6Wzyp+6lHpS8twkI 5N30OF8qYV4UUIxmSIEqVu61/Euuz/1LG93i8KWcbvbpbjAdvHiX+rvCjF0ON9R40KdBgd 30X7WCMvALabMCAFSaBF9Ri7XhkQ7Q4= Message-ID: <2e1bef30-3227-5137-cab8-5dbd7011f39c@greensocs.com> Date: Thu, 24 Feb 2022 12:43:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v4 13/14] hw/mem/system-memory: add a memory sysbus device Content-Language: en-US-large To: Igor Mammedov References: <20220223090706.4888-1-damien.hedde@greensocs.com> <20220223090706.4888-14-damien.hedde@greensocs.com> <20220223104450.196e9624@redhat.com> <9d0cfe90-01bc-6008-664f-74bdaa9c145c@greensocs.com> <20220224105521.1b760212@redhat.com> From: Damien Hedde In-Reply-To: <20220224105521.1b760212@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=5.135.226.135; envelope-from=damien.hedde@greensocs.com; helo=beetle.greensocs.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, 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: , Cc: Ani Sinha , edgari@xilinx.com, mark.burton@greensocs.com, qemu-devel@nongnu.org, "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/24/22 10:55, Igor Mammedov wrote: > On Wed, 23 Feb 2022 11:19:49 +0100 > Damien Hedde wrote: > >> On 2/23/22 10:44, Igor Mammedov wrote: >>> On Wed, 23 Feb 2022 10:07:05 +0100 >>> Damien Hedde wrote: >>> >>>> This device can be used to create a memory wrapped into a >>>> sysbus device. >>>> This device has one property 'readonly' which allows >>>> to choose between a ram or a rom. >>>> >>> >>>> The purpose for this device is to be used with qapi command >>>> device_add. >>> that's the way to add a device to QEMU but a don't actual >>> purpose described here, i.e. how board will use this >>> device/actual usecase and how it will be wired to board >>> and why it does have to be a sysbus device. >>> >> Sorry, this was unclear. >> >> It is a sysbus device in order to use it like any other sysbus device. >> The memory region it contains is exposed as a sysbus mmio. > > aside of that sysbus is legacy fictional bus (albeit widely used), > it doesn't scale to non sysbus devices (me thinking about buss-less > pc-dimm & co) since eventually we would like to create mainstream > machine types via QMP as well. > >> I can replace the commit message by the following paragraph: >> >> Boards instantiate memories by creating memory region objects which is >> not possible using QAPI commands. > > That's not entirely true, you can use object-add with hostmem backends > which do provide a means to allocate memory_region. > (there is no rom hostmem backend probably (i.e. one that return rom memory region) > but that could be added). > Another benefit of approach is that one can replace backing > memory any other backend (file/memfd/pmem...) without affecting > device model. I'm not familiar with memory backends. I need to take a look at them. > >> To create a memory, the user can instantiate and map this device by >> issuing the following commands: >> device_add driver=sysbus-memory size=0x1000 id=someram >> sysbus-mmio-map device=someram addr=0 > > I'd imagine more generic approach would look like: > > object-add memory-backend-ram,id=mem1,size=0x1000,other_backend_twiks > device_add memdevice_frontend,memdev=mem1,addr=0x0 > > where [pre]plug hooks in machine can map device to > an appropriate address space/place at device realize time. > (see memory_device_[pre_]plug() for starters). > We cannot rely on hooks the machine would define, because we start from an empty machine. So anything must come from qapi and we would need to do something like that I suppose: object-add memory-backend-ram,id=mem1,size=0x1000,other_backend_twiks device_add sysbus-memory-frontend,memdev=mem1,id=memdev_fe sysbus-mmio-map device=memdev_fe addr=0 Thanks, -- Damien