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 phobos.denx.de (phobos.denx.de [85.214.62.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C6C31C677F1 for ; Fri, 13 Jan 2023 10:44:25 +0000 (UTC) Received: from h2850616.stratoserver.net (localhost [IPv6:::1]) by phobos.denx.de (Postfix) with ESMTP id 176F485160; Fri, 13 Jan 2023 11:44:24 +0100 (CET) Authentication-Results: phobos.denx.de; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: phobos.denx.de; spf=pass smtp.mailfrom=u-boot-bounces@lists.denx.de Received: by phobos.denx.de (Postfix, from userid 109) id 3486E85160; Fri, 13 Jan 2023 11:44:23 +0100 (CET) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by phobos.denx.de (Postfix) with ESMTP id D209D85156 for ; Fri, 13 Jan 2023 11:44:19 +0100 (CET) Authentication-Results: phobos.denx.de; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: phobos.denx.de; spf=pass smtp.mailfrom=abdellatif.elkhlifi@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6872EFEC; Fri, 13 Jan 2023 02:45:01 -0800 (PST) Received: from e121910.cambridge.arm.com (unknown [10.57.46.90]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6E6B43F67D; Fri, 13 Jan 2023 02:44:18 -0800 (PST) Date: Fri, 13 Jan 2023 10:44:15 +0000 From: Abdellatif El Khlifi To: Simon Glass Cc: u-boot@lists.denx.de, nd@arm.com, robh@kernel.org Subject: Re: [PATCH v8 03/10] arm_ffa: introduce Arm FF-A low-level driver Message-ID: <20230113104415.GA22133@e121910.cambridge.arm.com> References: <20221124132115.GA393@e121910.cambridge.arm.com> <20221219111251.GA22370@e121910.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.39 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" X-Virus-Scanned: clamav-milter 0.103.6 at phobos.denx.de X-Virus-Status: Clean On Thu, Jan 12, 2023 at 04:43:32PM -0700, Simon Glass wrote: > Hi Rob, > > On Wed, 11 Jan 2023 at 19:10, Rob Herring wrote: > > > > On Mon, Dec 19, 2022 at 1:21 PM Simon Glass wrote: > > > > > > Hi Abdellatif, > > > > > > On Mon, 19 Dec 2022 at 04:12, Abdellatif El Khlifi > > > wrote: > > > > > > > > On Mon, Dec 05, 2022 at 09:49:30AM -0600, Rob Herring wrote: > > > > > On Sun, Dec 4, 2022 at 1:22 PM Simon Glass wrote: > > > > > > > > > > > > Hi Rob, > > > > > > > > > > > > On Tue, 29 Nov 2022 at 05:22, Rob Herring wrote: > > > > > > > > > > > > > > On Fri, Nov 25, 2022 at 3:18 PM Simon Glass wrote: > > > > > > > > > > > > > > > > Hi Abdellatif, > > > > > > > > > > > > > > > > On Thu, 24 Nov 2022 at 06:21, Abdellatif El Khlifi wrote: > > > > > > > > > > > > > > > > > > On Tue, Nov 22, 2022 at 07:09:16PM -0700, Simon Glass wrote: > > > > > > > > > > should be called 'priov' and should beHi Abdellatif, > > > > > > > > > > > > > > > > > > > > > > > > > > [..] > > > > > > > > > > > > > > > > > > > +/** > > > > > > > > > > > + * ffa_device_get - create, bind and probe the arm_ffa device > > > > > > > > > > > + * @pdev: the address of a device pointer (to be filled when the arm_ffa bus device is created > > > > > > > > > > > + * successfully) > > > > > > > > > > > + * > > > > > > > > > > > + * This function makes sure the arm_ffa device is > > > > > > > > > > > + * created, bound to this driver, probed and ready to use. > > > > > > > > > > > + * Arm FF-A transport is implemented through a single U-Boot > > > > > > > > > > > + * device managing the FF-A bus (arm_ffa). > > > > > > > > > > > + * > > > > > > > > > > > + * Return: > > > > > > > > > > > + * > > > > > > > > > > > + * 0 on success. Otherwise, failure > > > > > > > > > > > + */ > > > > > > > > > > > +int ffa_device_get(struct udevice **pdev) > > > > > > > > > > > +{ > > > > > > > > > > > + int ret; > > > > > > > > > > > + struct udevice *dev = NULL; > > > > > > > > > > > + > > > > > > > > > > > + ret = device_bind(dm_root(), DM_DRIVER_GET(arm_ffa), FFA_DRV_NAME, NULL, ofnode_null(), > > > > > > > > > > > + &dev); > > > > > > > > > > > > > > > > > > > > Please add a DT binding. Even if only temporary, we need something for this. > > > > > > > > > > > > > > > > > > Thanks for the feedback. I'm happy to address all the comments. > > > > > > > > > > > > > > > > > > Regarding DT binding and FF-A discovery. We agreed with Linaro and Rob Herring > > > > > > > > > about the following: > > > > > > > > > > > > > > > > > > - DT is only for what we failed to make discoverable. For hardware, we're stuck > > > > > > > > > with it. We shouldn't repeat that for software interfaces. This approach is > > > > > > > > > already applied in the FF-A kernel driver which comes with no DT support and > > > > > > > > > discovers the bus with bus_register() API [1]. > > > > > > > > > > > > > > > > This may be the UEFI view, but it is not how U-Boot works. This is not something we are 'stuck' with. It is how we define what is present on a device. This is how the PCI bus works in U-Boot. It is best practice in U-Boot to use the device tree to make this things visible and configurable. Unlike with Linux there is no other way to provide configuration needed by these devices. > > > > > > > > > > > > > > Where do you get UEFI out of this? > > > > > > > > > > > > I assume it was UEFI as there was no discussion about this in U-Boot. > > > > > > Which firmware project was consulted about this? > > > > > > > > > > > > > > > > > > > > It is the discoverability of hardware that is fixed (and we are stuck > > > > > > > with). We can't change hardware. The disoverability may be PCI > > > > > > > VID/PID, USB device descriptors, or nothing. We only use DT when those > > > > > > > are not sufficient. For a software interface, there is no reason to > > > > > > > make them non-discoverable as the interface can be fixed (at least for > > > > > > > new things like FF-A). > > > > > > > > > > > > Here I am talking about the controller itself, the top-level node in > > > > > > the device tree. For PCI this is a device tree node and it should be > > > > > > the same here. So I am not saying that the devices on the bus need to > > > > > > be in the device tree (that can be optional, but may be useful in some > > > > > > situations where it is status and known). > > > > > > > > > > Sure, the PCI host bridges are not discoverable, have a bunch of > > > > > resources, and do need to be in DT. The downstream devices only do if > > > > > they have extra resources such as when a device is soldered down on a > > > > > board rather than a standard slot. > > > > > > > > > > > We need something like: > > > > > > > > > > > > ff-a { > > > > > > compatible = "something"; > > > > > > }; > > > > > > > > > > > > I don't know what mechanism is actually used to communicate with it, > > > > > > but that will be enough to get the top-level driver started. > > > > > > > > > > There's discovery of FF-A itself and then discovery of FF-A features > > > > > (e.g. partitions). Both of those are discoverable without DT. The > > > > > first is done by checking the SMCCC version, then checking for FF-A > > > > > presence and features. Putting this into DT is redundant. Worse, what > > > > > if they disagree? > > > > > > > > Hi Simon, > > > > > > > > Do you agree with Rob, Ilias and myself that it makes more sense > > > > FF-A bus is discovered without a DT node and following the same approach as > > > > Linux ? (FF-A bus doesn't have a HW controller and is a purely SW bus, > > > > no configuration/description needed at DT level). > > > > > > > > Your suggestions are always welcome. > > > > > > I'm sorry I don't agree with that. It does need a compatible string, > > > like PCI has. You can just add it in U-Boot if Linux won't accept the > > > binding. > > > > It's not like PCI as the host side of PCI has non-discoverable resources. > > OK I see. It is certainly an edge case. > > > > > This all could have been designed better, but hindsight is 20/20 and > > things evolved step by step. There are a bunch of firmware services > > that are all behind SMCCC. The first (upstream) was PSCI. IIRC, SMCCC > > was invented a bit after that, but generalized PSCI for other > > services. Since then more have been added. More services get added one > > by one and yes we added bindings for them. Because what's one more... > > But that really needs to stop. We're stuck with h/w that's not > > discoverable, there's zero reason to do that with s/w interfaces. If > > we could redo everything, we'd have a node for SMCCC and that's it > > unless there's h/w resources provided to the rest of DT. But we can't, > > so SMCCC is discovered by the presence of PSCI. > > I understand the background here, but if we don't take a stand on > this, this sort of thing will continue. Just because something works > in Linux does not mean that the binding (or lack of it) is good. > > The reasons to do this are: > - avoids needing to manually call device_bind() > - avoids extra plumbing in U-Boot > - provides visibility into what is in the system, by looking at the > DT, like documentation > - DT is how devices are bound in U-Boot > > You can see the problem if you look at ffa_device_get(). It is called > from ffa_bus_discover() which is a new addition into the board_init > list. We are trying to remove this list and certainly don't want new > things added!! Hi Simon, As stated in the v8 patchset cover letter [1] and readme [2], the FF-A bus is discoverable on demand at runtime. Clients (such as EFI) can discover the FF-A bus using ffa_bus_discover() API which triggers the discovery process. We no longer use the board_init list to discover the FF-A bus. Please refer to the v8 patchset for the review. Cheers [1]: https://lore.kernel.org/all/20221122131751.22747-1-abdellatif.elkhlifi@arm.com/ [2]: https://lore.kernel.org/all/20221122131751.22747-4-abdellatif.elkhlifi@arm.com/#Z31doc:arch:arm64.ffa.rst > > We don't need to change this in the Linux implementation, just add a > top-level DT node for U-Boot. I don't understand why that is such a > big problem? > > Regards, > Simon