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 233C9C04AB5 for ; Thu, 6 Jun 2019 15:40:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0115A206BB for ; Thu, 6 Jun 2019 15:40:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729449AbfFFPkz (ORCPT ); Thu, 6 Jun 2019 11:40:55 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:49228 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729137AbfFFPky (ORCPT ); Thu, 6 Jun 2019 11:40:54 -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 0760DA78; Thu, 6 Jun 2019 08:40:54 -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 5D8473F690; Thu, 6 Jun 2019 08:40:52 -0700 (PDT) Date: Thu, 6 Jun 2019 16:40:45 +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: <20190606154045.GA2429@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> <20190606125140.GB26273@e107155-lin> 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 Thu, Jun 06, 2019 at 10:20:40AM -0500, Jassi Brar wrote: > On Thu, Jun 6, 2019 at 7:51 AM Sudeep Holla wrote: > > > > > > 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. > > > Can you please share the code? Or is it no more available? > > > 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). > > > I don't see why the overhead should increase noticeably. > Simple, if 2 protocols share the same channel, then the requests are serialised. E.g. if bits 0 and 1 are allocated for protocol#1 and bits 2 and 3 for protocol#2 and protocol#1 has higher latency requirements like sched-governor DVFS and there are 3-4 pending requests on protocol#2, then the incoming request for protocol#1 is blocked. > > 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. > > > Please suggest how is SCMI supposed to work on ~15 controllers > upstream (except tegra-hsp) ? > Do you mean we have to implement platform layer to make it work ? That's not necessary IMO. > > It also avoids coming up with virtual DT > > nodes for this layer of abstract which I am completely against. > > > I don't see why virtual DT nodes would be needed for platform layer. So how will 2 or more different users of the same mailbox identify the bits allocated for them ? -- Regards, Sudeep