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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id F1569C433F5 for ; Sat, 4 Dec 2021 04:24:40 +0000 (UTC) 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:Cc:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=uFo31w+RStUAsgb4RHdTz9ozQ5/V35aYfhVzKS6AoQk=; b=JEhYNqjujyZlBM kgXw3ciPTKQksTf2+tS0G8XtwJqSZntHPvZNSmuouM20PXM+z8EYp00Su+lLCEZEYFpxNGKwkPXg3 a4x8+pZzS5AF9HerwBi/w3Y+Kzht4YAYCyJ3zdudoDIYumgPVkhobtikkxymKUOYTV+B1lQf16K46 I+2mg0cBawn+QNdFUqvPc9DmZ5xBUIWcvahVSQq0QVWoLgEJIZQhHipZGR0s8u7jYO4tyXxyQN30x wBygHkb7nId/oMemYwsfI5T267qENFASx1mVBeGt0V3X4DRI+zs1CjT4K8cZvgLdhrv27Ec6ypta3 +y7lnuu+5ovcl5o5ilDQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mtMb4-00HUbt-Vg; Sat, 04 Dec 2021 04:24:27 +0000 Received: from mail-wm1-x336.google.com ([2a00:1450:4864:20::336]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mtMb1-00HUbS-Po for linux-riscv@lists.infradead.org; Sat, 04 Dec 2021 04:24:25 +0000 Received: by mail-wm1-x336.google.com with SMTP id o19-20020a1c7513000000b0033a93202467so3717534wmc.2 for ; Fri, 03 Dec 2021 20:24:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brainfault-org.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=CDC6pBpyKnlU0o+d49B8awXmO6YaYMKcz0TAFhInA14=; b=uc8UhsxX+92u5QZMtVFBJ1ml6gWw9QqehwOr+oTJCDEX9b8NGDwnBc/RjisWw21q2t 3lMolSkvZCSGGDtPTsQ1IIMxx8w41k44wPf3rgIW2IwGV0X1G5drgJNs7GWNuOJcEpDk qkLuzCvLj5vJU3iMOT8H+VTDyyHW345gnBn2NsCls45NGHABaQmCA0dCYCZ3cFQ5RAKt CMvMpAlKF08+wW+Jy0bTwQFIoHXmrvFCx1MX/1weSrCqoSMSTTlGtab86hWOaYUh17IS lhQyXD4UT0gRDz8q1RzQjdyh6tBHvnWcTXZKUKq6i722rm4IUIIHqxtH2j5OMWSGN9ol 7uEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=CDC6pBpyKnlU0o+d49B8awXmO6YaYMKcz0TAFhInA14=; b=A2gX0w/4QLn7Tmx+0ZfowNifPt0ci6GwuEABt8gPVi2HukXdMRPMftM2dcrQy9+28v /d66sV9uffb74avA4rTjIlRW+20uZInVqFCzxjgbHH5nuKaxIQTLAFU0BP47UXM76cPp emKTwpREt70mZNXI2hCa7QCGTl3r57u4s03STvpwZbRO21AcOUR4XE3wcqAub9hhf7FQ +EvtyoVi4kBdrPLrKaKdKvRPuf+4bjsMTyzjOwYEYtLmTRL1MEF/Jn8e8EYfEH8zJ9Yu 3D3607RaG19DFD++knh0bVVN5RFwBjKTWWIOjp994MwCgTffQW0DhoMus1j94sT9ir2/ u5fw== X-Gm-Message-State: AOAM5307RGWot8OSs25JYhpfL524vZbsr+e+HFHKA7+qLKJKehZ3R6wf lYzd3GlwU39XFQdKMqOF/WJyqmLrv5VLD/4bgD1FLg== X-Google-Smtp-Source: ABdhPJwLBjjw+WQUry26a/ymi+N+xm7jefu0nOAXo2bK+G04Wzh67KtlDNZwNrQBTD8n6Q8FL5Z6tICK6VMqWTnW7UY= X-Received: by 2002:a7b:c7cd:: with SMTP id z13mr20716083wmk.59.1638591861075; Fri, 03 Dec 2021 20:24:21 -0800 (PST) MIME-Version: 1.0 References: <20211202150515.GA97518@sunil-ThinkPad-T490> <89d42547-ec36-5f84-88d1-fd65d891488c@canonical.com> <6d9f131d-b3e8-18df-a9b6-6aaac881eb65@canonical.com> <6fccad4e-b579-25ed-6bf3-2fb2a968b243@canonical.com> <7416157e-50d1-3664-7df0-2a45e29cd8c1@canonical.com> In-Reply-To: <7416157e-50d1-3664-7df0-2a45e29cd8c1@canonical.com> From: Anup Patel Date: Sat, 4 Dec 2021 09:54:09 +0530 Message-ID: Subject: Re: Question regarding "boot-hartid" DT node To: Heinrich Schuchardt Cc: Atish Patra , Abner Chang , Heinrich Schuchardt , Jessica Clarke , Palmer Dabbelt , sunil.vl@gmail.com, linux-riscv , Sunil V L , Ard Biesheuvel X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211203_202423_876871_25F2E8D6 X-CRM114-Status: GOOD ( 66.52 ) X-BeenThere: linux-riscv@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-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Sat, Dec 4, 2021 at 7:17 AM Heinrich Schuchardt wrote: > > > > On 12/4/21 01:44, Atish Patra wrote: > > On Fri, Dec 3, 2021 at 10:45 AM Heinrich Schuchardt wrote: > >> > >> On 12/3/21 11:53 AM, Heinrich Schuchardt wrote: > >>> On 12/3/21 11:13, Ard Biesheuvel wrote: > >>>> On Thu, 2 Dec 2021 at 20:29, Atish Patra wrote: > >>>>> > >>>>> On Thu, Dec 2, 2021 at 9:05 AM Heinrich Schuchardt > >>>>> wrote: > >>>>>> > >>>>>> On 12/2/21 17:58, Ard Biesheuvel wrote: > >>>>>>> On Thu, 2 Dec 2021 at 17:53, Heinrich Schuchardt > >>>>>>> wrote: > >>>>>>>> > >>>>>>>> On 12/2/21 17:20, Ard Biesheuvel wrote: > >>>>>>>>> On Thu, 2 Dec 2021 at 16:05, Sunil V L > >>>>>>>>> wrote: > >>>>>>>>>> > >>>>>>>>>> Hi All, > >>>>>>>>>> I am starting this thread to discuss about the > >>>>>>>>>> "boot-hartid" DT node > >>>>>>>>>> that is being used in RISC-V Linux EFI stub. > >>>>>>>>>> > >>>>>>>>>> As you know, the boot Hart ID is passed in a0 register to > >>>>>>>>>> the kernel > >>>>>>>>>> and hence there is actually no need to pass it via DT. > >>>>>>>>>> However, since > >>>>>>>>>> EFI stub follows EFI application calling conventions, it > >>>>>>>>>> needs to > >>>>>>>>>> know the boot Hart ID so that it can pass it to the proper > >>>>>>>>>> kernel via > >>>>>>>>>> a0. For this issue, the solution was to add > >>>>>>>>>> "/chosen/boot-hartid" in > >>>>>>>>>> DT. Both EDK2 and u-boot append this node in DT. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> I think this was a mistake tbh > >>>>>>>>> > >>>>>>>>>> But above approach causes issue for ACPI since ACPI > >>>>>>>>>> initialization > >>>>>>>>>> happens late in the proper kernel. Same is true even if we > >>>>>>>>>> pass this > >>>>>>>>>> information via SMBIOS. > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> It would be better to define a RISCV specific EFI protocol that the > >>>>>>>>> stub can call to discover the boot-hartid value. That wat, it can > >>>>>>>>> pass > >>>>>>>>> it directly, without having to rely on firmware tables. > >>>>>>>> > >>>>>>>> As discovering the current process' hartid is not a UEFI specific > >>>>>>>> task > >>>>>>>> SBI would be a better fit. > >>>>>>>> > >>>>>>> > >>>>>>> I disagree. The OS<->loader firmware interface is UEFI not SBI. So if > >>>>>>> the EFI stub needs to ask the firmware which boot-hartid it should > >>>>>>> pass in A0, it should use a EFI protocol and nothing else. > >>>>>>> > >>>>>>> Whether or not the loader/firmware *implements* this EFI protocol by > >>>>>>> calling into SBI is a different matter (and likely the best choice). > >>>>>>> But that does not mean the EFI stub should make SBI calls directly. > >>>>>>> > >>>>>> > >>>>>> The EFI stub does not need the boot-hartid. It is the main Linux kernel > >>>>>> that does. And that kernel already implements SBI calls. > >>>>>> > >>>>>> The main kernel could just try to read CSR mhartid which fails in > >>>>>> S-mode > >>>>>> and the SBI could emulate it. > >>>>> > >>>>> New SBI extension should be added only if there is no other way to > >>>>> solve a generic > >>> > >>> I am not sure this feature would be implemented as SBI extension or as a > >>> CSR emulation. Cf. sbi_emulate_csr_read(). But anyway it would require > >>> an update of the SBI specification. > >>> > >>>>> problem. The boot hartid issue is very specific to efi booting only. > >>>>> Any system that doesn't require > >>> > >>> The boot hartid is not EFI related at all. A firmware running single > >>> threaded does not need this information. > >>> > >>> Information about the boot hartid is a general OS need. > >>> > >>> I am wondering why S-mode software should not have a generic means to > >>> find out on which hart it is currently running. > >>> > >>>>> EFI booting won't need it. Even for EFI booting, we have other > >>>>> approaches already proposed > >>>>> to solve it. That's why, SBI extension should be the last resort > >>>>> rather than first. > >>>>> > >>>>> I think an RISC-V specific EFI protocol as suggested by Ard should > >>>>> work for all the cases. > >>>>> Is there a case where you think it may not work ? U-Boot & EDK2 > >>>>> already stores the boot hartid. > >>>>> They just implement that protocol and pass the hartid to the caller. > >>>>> We do need to support it in the grub though. > >>>>> > >>>> > >>>> Why would GRUB care about this? The EFI stub will call into the > >>>> underlying firmware to invoke the protocol, GRUB is just a loader with > >>>> a fancy menu that allows you to select which image to load, no? > >>> > >>> This is a related discussion: > >>> > >>> https://github.com/tekkamanninja/grub/commit/be9d4f1863a1fcb1cbbd2f867309457fade8be73#commitcomment-60851029 > >>> > > > > Yes!! Thanks for refreshing the memory. It seems after 2 years, we are > > still debating the same topic :). > > Let me summarize the thread. There are multiple ways for EFI stub code > > to retrieve the boot hartid. > > > > 1. EFI variables - This is what Henerich proposed last time. Ard > > suggested that EFI configuration tables are better candidates than EFI > > variables. > > 2. DT modification - This was preferred over the configuration table > > at that time given because RISC-V was DT only at that time. > > We already had all the infrastructure > > around DT. Thus, DT seemed to be a natural choice then. > > It works now for existing setup > > however, the DT approach will not work for systems with ACPI support. > > Adding a similar entry in ACPI tables > > is possible but adding ACPI support in EFI stub is not trivial. > > 3. SMBIOS - Only for platforms with SMBIOS support. SMBIOS is not > > mandatory and adding SMBIOS support in EFI stub is not trivial. > > 4. SBI - As I mentioned before, this is an EFI specific > > problem because EFI stub doesn't know what the boot hartid is. Thus, > > it should be solved > > in an EFI specific way. An SBI extension for > > such features may not be acceptable as the non-EFI booting method > > works fine without the SBI extension. > > 5. RISC-V specific EFI configuration table or protocol: Ard suggested > > EFI configuration table last time. Earlier in this thread, EFI > > protocol was suggested. > > My personal preference has always been one of > > these as it solves the problem for all EFI booting methods > > for platforms-os > > combination(DT/ACPI-Linux/FreeBSD) in an EFI specific way. > > > > @Heinrich: Do you see any issue with the EFI configuration table or > > protocol to retrieve the boot hartid? > > There is nothing technical stopping us from implementing either option. > > We could simply reuse the EFI Device Tree Fixup Protocol > (https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL) implemented in > U-Boot and already used by systemd-boot. Pass a devicetree (which may be > empty) to the Fixup() method and it will add the /chosen node with the > boot-hartid parameter. > > The EFI stub anyway creates a new device-tree to pass the memory map to > the kernel in the ACPI case (function update_fdt()). Calling the EFI > Device Tree Fixup Protocol could be easily added. Are you suggesting that DTB (skeletal or full-blown) will always be there when booting the kernel as an EFI application ? If yes then we are indirectly mandating skeletal DTB for UEFI+ACPI system. Regards, Anup > > Best regards > > Heinrich > > > > > My only concern with the RISC-V EFI protocol is that Ard suggested it > > doesn't need a modification in UEFI spec. > > Where should we document it in this case ? We can't document it in > > Linux or EBBR. > > Because, this is a protocol that server systems and other non-Linux OS > > will also use. > > We can define it in the RISC-V platform spec. But that's not the usual > > place where somebody will look for the definition of such protocol. > > > > Wouldn't it be better to standardize it in UEFI spec ? The UEFI spec > > already has ARCH specific protocols/config tables. > > > >>> > >>> If GRUB loads a devicetree it will anyway have to call into the firmware > >>> for fixups. These will include adding the boot-hartid. > >>> > >>>> > >>>>> @Heinrich Schuchardt > >>>>> I vaguely remember you proposed something similar when we discussed > >>>>> this first during FOSDEM. > >>>>> I can't recall why it was abandoned in favor of the DT approach which > >>>>> works. But, > >>>>> it is not an ideal solution considering RISC-V ACPI support is already > >>>>> on the way. > >>>>> > >>>>> Do you have a link to the older thread where this thing was discussed ? > >>> > >>> Unfortunately I cannot find anything. > >> > >> I assume Atish referred to this thread: > >> > >> https://patchwork.ozlabs.org/project/uboot/patch/20200205055334.4072-1-xypron.glpk@gmx.de/ > >> > >> Best regards > >> > >> Heinrich > >> > >> _______________________________________________ > >> linux-riscv mailing list > >> linux-riscv@lists.infradead.org > >> http://lists.infradead.org/mailman/listinfo/linux-riscv > > > > > > _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv