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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i2ySh-0001n1-7l; Wed, 28 Aug 2019 13:58:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i2ySe-0001lw-KS for linux-arm-kernel@lists.infradead.org; Wed, 28 Aug 2019 13:58:10 +0000 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 60EBC28; Wed, 28 Aug 2019 06:58:06 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E58733F246; Wed, 28 Aug 2019 06:58:04 -0700 (PDT) Date: Wed, 28 Aug 2019 14:58:02 +0100 From: Sudeep Holla To: Peng Fan Subject: Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox Message-ID: <20190828135802.GB21614@e107155-lin> References: <1567004515-3567-1-git-send-email-peng.fan@nxp.com> <1567004515-3567-2-git-send-email-peng.fan@nxp.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1567004515-3567-2-git-send-email-peng.fan@nxp.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190828_065808_760935_13996A8E X-CRM114-Status: GOOD ( 27.16 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "mark.rutland@arm.com" , "devicetree@vger.kernel.org" , "f.fainelli@gmail.com" , "andre.przywara@arm.com" , "jassisinghbrar@gmail.com" , "linux-kernel@vger.kernel.org" , "robh+dt@kernel.org" , dl-linux-imx , Sudeep Holla , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Aug 28, 2019 at 03:02:58AM +0000, Peng Fan wrote: > From: Peng Fan > > The ARM SMC/HVC mailbox binding describes a firmware interface to trigger > actions in software layers running in the EL2 or EL3 exception levels. > The term "ARM" here relates to the SMC instruction as part of the ARM > instruction set, not as a standard endorsed by ARM Ltd. > > Signed-off-by: Peng Fan > --- > .../devicetree/bindings/mailbox/arm-smc.yaml | 125 +++++++++++++++++++++ > 1 file changed, 125 insertions(+) > create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.yaml > > diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.yaml b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml > new file mode 100644 > index 000000000000..f8eb28d5e307 > --- /dev/null > +++ b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml > @@ -0,0 +1,125 @@ > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/mailbox/arm-smc.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: ARM SMC Mailbox Interface > + > +maintainers: > + - Peng Fan > + > +description: | > + This mailbox uses the ARM smc (secure monitor call) and hvc (hypervisor > + call) instruction to trigger a mailbox-connected activity in firmware, > + executing on the very same core as the caller. By nature this operation > + is synchronous and this mailbox provides no way for asynchronous messages > + to be delivered the other way round, from firmware to the OS, but > + asynchronous notification could also be supported. What do you mean by that ? I would prefer to drop the above line unless I am missing something. IMO it contradicts the previous statement less you elaborate more on this. > However the value of > + r0/w0/x0 the firmware returns after the smc call is delivered as a received > + message to the mailbox framework, so a synchronous communication can be > + established, for a asynchronous notification, no value will be returned. I assume you refer to asynchronous communication from OS to firmware in the above statement and "not asynchronous notification" from firmware to OS. > + The exact meaning of both the action the mailbox triggers as well as the > + return value is defined by their users and is not subject to this binding. > + > + One use case of this mailbox is the SCMI interface, which uses shared memory > + to transfer commands and parameters, and a mailbox to trigger a function > + call. This allows SoCs without a separate management processor (or when > + such a processor is not available or used) to use this standardized > + interface anyway. > + Not sure if reference to SCMI is needed at all but I don't have any objections to it, just thought worth mentioning. > + This binding describes no hardware, but establishes a firmware interface. > + Upon receiving an SMC using one of the described SMC function identifiers, > + the firmware is expected to trigger some mailbox connected functionality. > + The communication follows the ARM SMC calling convention. > + Firmware expects an SMC function identifier in r0 or w0. The supported > + identifiers are passed from consumers, or listed in the the arm,func-ids > + properties as described below. The firmware can return one value in > + the first SMC result register, it is expected to be an error value, > + which shall be propagated to the mailbox client. > + > + Any core which supports the SMC or HVC instruction can be used, as long as > + a firmware component running in EL3 or EL2 is handling these calls. > + Other than the above points, I am fine with it. Once fixed, Reviewed-by: Sudeep Holla Note I haven't reviewed the yaml scheme, but just binding in general. -- Regards, Sudeep _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel