From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yong Wu Subject: Re: [PATCH v3 13/15] memory: mtk-smi: Get rid of need_larbid Date: Mon, 3 Dec 2018 16:40:51 +0800 Message-ID: <1543826451.23023.35.camel@mhfsdcap03> References: <1542422142-30688-1-git-send-email-yong.wu@mediatek.com> <1542422142-30688-14-git-send-email-yong.wu@mediatek.com> <21767ceb-1db5-045f-06ac-29c57f1a74a5@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <21767ceb-1db5-045f-06ac-29c57f1a74a5@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Matthias Brugger Cc: Joerg Roedel , Robin Murphy , Rob Herring , youlin.pei@mediatek.com, devicetree@vger.kernel.org, Nicolas Boichat , arnd@arndb.de, srv_heupstream@mediatek.com, Will Deacon , linux-kernel@vger.kernel.org, Tomasz Figa , iommu@lists.linux-foundation.org, linux-mediatek@lists.infradead.org, Arvind Yadav , yingjoe.chen@mediatek.com, linux-arm-kernel@lists.infradead.org, YT.shen@mediatek.com List-Id: iommu@lists.linux-foundation.org On Mon, 2018-12-03 at 00:04 +0100, Matthias Brugger wrote: > > On 17/11/2018 03:35, Yong Wu wrote: > > The "mediatek,larb-id" has already been parsed in MTK IOMMU driver. > > It's no need to parse it again in SMI driver. Only clean some codes. > > This patch is fit for all the current mt2701, mt2712, mt7623, mt8173 > > and mt8183. > > I'm trying to understand why we need the mediatek,larb-id at all. From what I > understand as long as the mediatek larbs described in the iommu are ordered > (larb0, larb1, larb2, etc) we actually get the same value as defined by > mediatek,larb-id. At least this holds for all present implementations. > > On the other hand I don't see where the mtk_iommu_v1 driver actually parses the > larb-id, can you please help to understand: > > 1) why we need the larb-id at all Actually only mt2712 which have 2 M4U HW need "mediatek,larb-id". This is larbs in the m4u0/1 dtsi node of mt2712: m4u0 { mediatek,larbs = <&larb0 &larb1 &larb2 &larb3 &larb6>;} m4u1 { mediatek,larbs = <&larb4 &larb5 &larb7>;} the id don't increase one by one, M4U have to get the larbid with the help of "mediatek,larb-id". (The m4u/smi dtsi patch of mt2712 will be send with some other modules, maybe in this week.) > 2) how this will work if we do not parse the larb-id for v1 iommu at all As you said above and I also have wrote that the larbid "must sort according to the local arbiter index" in the "mediatek,larbs" description of dt-binding. All the M4U except mt2712 could ignore "mediatek,larb-id". the v1 iommu also should be ok. I'm not sure whether we should change [1], if only reserving mt2712 there, we also should change the dtsi file of mt2701 and mt7623.or keep it as is. [1] https://elixir.bootlin.com/linux/v4.20-rc1/source/Documentation/devicetree/bindings/memory-controllers/mediatek,smi-larb.txt#L20 > > Thanks a lot, > Matthias > > > [snip]