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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 69928C433DF for ; Wed, 3 Jun 2020 18:28:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 421E62053B for ; Wed, 3 Jun 2020 18:28:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725882AbgFCS2L (ORCPT ); Wed, 3 Jun 2020 14:28:11 -0400 Received: from foss.arm.com ([217.140.110.172]:36694 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725821AbgFCS2L (ORCPT ); Wed, 3 Jun 2020 14:28:11 -0400 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 B9DF931B; Wed, 3 Jun 2020 11:28:10 -0700 (PDT) Received: from bogus (unknown [10.37.8.135]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9073D3F305; Wed, 3 Jun 2020 11:28:08 -0700 (PDT) Date: Wed, 3 Jun 2020 19:28:05 +0100 From: Sudeep Holla To: Bjorn Andersson Cc: Viresh Kumar , Jassi Brar , Arnd Bergmann , Rob Herring , Frank Rowand , Vincent Guittot , Sudeep Holla , linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU Message-ID: <20200603182805.GD23722@bogus> References: <0a50f0cf5593baeb628dc8606c523665e5e2ae6c.1589519600.git.viresh.kumar@linaro.org> <20200519012927.GT2165@builder.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200519012927.GT2165@builder.lan> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Bjorn, Thanks for the details response. On Mon, May 18, 2020 at 06:29:27PM -0700, Bjorn Andersson wrote: > On Thu 14 May 22:17 PDT 2020, Viresh Kumar wrote: > [...] I find this part nicely summarise your response. > > - With serialization, if we use only one channel as today at every > > priority, if there are 5 requests to send signal to the receiver and > > the dvfs request is the last one in queue (which may be called from > > scheduler's hot path with fast switching), it unnecessarily needs to > > wait for the first four transfers to finish due to the software > > locking imposed by the mailbox framework. This adds additional delay, > > maybe of few ms only, which isn't required by the hardware but just by > > the software and few ms can be important in scheduler's hotpath. > > > > So these 5 requests, are they conveyed by the signals [1,2,3,4,5] or > [BIT(0), BIT(1), BIT(2), BIT(3), BIT(4)]? > Latter in this case. IMO it is platform choice on how to use it. It is equally possible to send 2^31 different signals. But the receiver must also interpret it in the *exact* same way. In this case, the receiver which is platform firmware interprets as individual bit signals. > In the first case you have to serialize things given that e.g. signal 1 > immediately followed by 2 is indistinguishable from 3. > Agree and we are not proposing to break that use case. It exists in the driver/binding today and will continue as is. > If you signals are single-bit notifications then you don't need any > serialization. > Indeed, we are making use of that. -- Regards, Sudeep