From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752807AbeB1PG1 (ORCPT ); Wed, 28 Feb 2018 10:06:27 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:51336 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752250AbeB1PGX (ORCPT ); Wed, 28 Feb 2018 10:06:23 -0500 Subject: Re: [PATCH v5 08/13] iommu/rockchip: Control clocks needed to access the IOMMU To: JeffyChen , Rob Herring , Tomasz Figa Cc: "linux-kernel@vger.kernel.org" , Ricky Liang , simon xue , devicetree@vger.kernel.org, Heiko Stuebner , "open list:ARM/Rockchip SoC..." , "list@263.net:IOMMU DRIVERS" , Joerg Roedel , Mark Rutland , linux-arm-kernel@lists.infradead.org References: <20180124103516.2571-1-jeffy.chen@rock-chips.com> <20180124103516.2571-9-jeffy.chen@rock-chips.com> <20180130170515.3g6wtadqgmehxh5b@rob-hp-laptop> <5A72F7D2.1050201@rock-chips.com> <5A8FEBC6.4000408@rock-chips.com> <33d1d6bd-3455-5cad-6990-a9ca94063f3a@arm.com> <5A96A809.2020509@rock-chips.com> From: Robin Murphy Message-ID: <34a60ab2-a3af-3302-6612-740cba5460db@arm.com> Date: Wed, 28 Feb 2018 15:06:19 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <5A96A809.2020509@rock-chips.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/02/18 13:00, JeffyChen wrote: > Hi Robin, > > Thanks for your reply. > > On 02/28/2018 12:59 AM, Robin Murphy wrote: >>>> the rockchip IOMMU is part of the master block in hardware, so it needs >>>> to control the master's power domain and some of the master's clocks >>>> when access it's registers. >>>> >>>> and the number of clocks needed here, might be different between each >>>> IOMMUs(according to which master block it belongs), it's a little like >>>> our power domain: >>>> https://elixir.free-electrons.com/linux/latest/source/arch/arm64/boot/dts/rockchip/rk3399.dtsi#L935 >>>> >>>> >>>> >>>> >>>> i'm not sure how to describe this correctly, is it ok use something >>>> like >>>> "the same as it's master block"? >>> >>> would it make sense to add a property to specify the master who owns >>> the iommu, and we can get all clocks(only some of those clocks are >>> actually needed) from it in the of_xlate()? and we can also reuse the >>> clock-names of that master to build clk_bulk_data and log errors in >>> clk_bulk_get. >> >> I'm inclined to agree with Rob here - if we're to add anything to the >> binding, it should only be whatever clock inputs are defined for the >> IOMMU IP block itself. If Linux doesn't properly handle the interconnect >> clock hierarchy external to a particular integration, that's a separate >> issue and it's not the binding's problem. >> >> I actually quite like the hack of "borrowing" the clocks from >> dev->of_node in of_xlate() - you shouldn't need any DT changes for that, >> because you already know that each IOMMU instance only has the one >> master device anyway. > > Thanks:) but actually we are going to support sharing IOMMU between > multiple masters(one of them is the main master i think) in the newer > chips(not yet supported on upstream kernel)... Ha! OK, fair enough, back to the first point then... > So we might have to get all clocks from all masters, or find a way to > specify the main master...and for the multiple masters case, do it in > of_xlate() turns out to be a little racy...maybe we can add a property > to specify main master, and get it's clocks in probe()? I notice that the 4.4 BSP kernel consistently specifies "aclk" and "hclk" for the IOMMU instances - it feels unusual to say "why don't we follow the downstream binding?", but it does look a lot like what I would expect (I'd guess at one for the register slave interface and one for the master interface/general operation?) If we can implement conceptually-correct clock handling based on an accurate binding, which should cover most cases, and *then* look at hacking around those where it doesn't quite work in practice due to shortcomings elsewhere, that would be ideal, and of course a lot nicer than just jumping straight into piles of hacks. Robin.