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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B32EC04AB5 for ; Thu, 6 Jun 2019 12:51:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0A71B20866 for ; Thu, 6 Jun 2019 12:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727998AbfFFMvq (ORCPT ); Thu, 6 Jun 2019 08:51:46 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46832 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727310AbfFFMvp (ORCPT ); Thu, 6 Jun 2019 08:51:45 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2C15C374; Thu, 6 Jun 2019 05:51:45 -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 834683F5AF; Thu, 6 Jun 2019 05:51:43 -0700 (PDT) Date: Thu, 6 Jun 2019 13:51:41 +0100 From: Sudeep Holla To: Jassi Brar Cc: Mark Brown , Linux Kernel Mailing List , linux-arm-kernel@lists.infradead.org, Arnd Bergmann , Bjorn Andersson , Rob Herring , Sudeep Holla , Cristian Marussi Subject: Re: [PATCH 0/6] mailbox: arm_mhu: add support to use in doorbell mode Message-ID: <20190606125140.GB26273@e107155-lin> References: <20190531143320.8895-1-sudeep.holla@arm.com> <20190531165326.GA18115@e107155-lin> <20190603193946.GC2456@sirena.org.uk> <20190604093827.GA31069@e107533-lin.cambridge.arm.com> <20190605194636.GW2456@sirena.org.uk> 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) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 05, 2019 at 07:51:12PM -0500, Jassi Brar wrote: > On Wed, Jun 5, 2019 at 2:46 PM Mark Brown wrote: > > > > On Tue, Jun 04, 2019 at 10:44:24AM +0100, Sudeep Holla wrote: > > > On Mon, Jun 03, 2019 at 08:39:46PM +0100, Mark Brown wrote: > > > > > > > > > It feels like the issues with sharing access to the hardware and with the > > > > API for talking to doorbell hardware are getting tied together and > > > > confusing things. But like I say I might be missing something here. > > > > ... > > > > > So what I am trying to convey here is MHU controller hardware can be > > > used choosing one of the different transport protocols available and > > > that's platform choice based on the use-case. > > > > > The driver in the kernel should identify the same from the firmware/DT > > > and configure it appropriately. > > > > > It may get inefficient and sometime impossible to address all use-case > > > if we stick to one transport protocol in the driver and try to build > > > an abstraction on top to use in different transport mode. > > > > Right, what I was trying to get at was that it feels like the discussion > > is getting wrapped up in the specifics of the MHU rather than > > representing this sort of controller with multiple modes in the > > framework. > > > Usually when a controller could be used in more than one way, we > implement the more generic usecase. And that's what was done for MHU. That's debatable and we have done that so extensively so far. So what I am saying is to implement different modes not just one so that as many use-case are addressed. > Implementing doorbell scheme would have disallowed mhu platforms that > don't have any shmem between the endpoints. Now such platforms could > use 32bits registers to pass/get data. Meanwhile doorbells could be > emulated in client code. > Also, next version of MHU has many (100?) such 32bit registers per > interrupt. Clearly those are not meant to be seen as 3200 doorbells, > but as message passing windows. (or maybe that is an almost different > controller because of the differences) > I disagree. It's configurable and vendors can just choose 2 instead of 100s as you mentioned based on the use-case and needs. So we will still need the same there. > BTW, this is not going to be the end of SCMI troubles (I believe > that's what his client is). SCMI will eventually have to be broken up > in layers (protocol and transport) for many legit platforms to use it. > That is mbox_send_message() will have to be replaced by, say, > platform_mbox_send() in drivers/firmware/arm_scmi/driver.c OR the > platforms have to have shmem and each mailbox controller driver (that > could ever be used under scmi) will have to implement "doorbell > emulation" mode. That is the reason I am not letting the way paved for > such emulations. > While I don't dislike or disagree with separate transport in SCMI which I have invested time and realised that I will duplicate mailbox framework at the end. So I am against it only because of duplication and extra layer of indirection which has performance impact(we have this seen in sched governor for DVFS). So idea wise, it's good and I don't disagree with practically seen performance impact. Hence I thought it's sane to do something I am proposing. It also avoids coming up with virtual DT nodes for this layer of abstract which I am completely against. -- Regards, Sudeep