linux-kernel - Re: [PATCH v13 0/4] Mediatek MT8173 CMDQ support

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Date:   Thu, 25 Aug 2016 19:12:57 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Horng-Shyang Liao <hs.liao@...iatek.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        Sascha Hauer <kernel@...gutronix.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Nicolas Boichat <drinkcat@...omium.org>,
        CK HU <ck.hu@...iatek.com>,
        cawa cheng <cawa.cheng@...iatek.com>,
        Bibby Hsieh <bibby.hsieh@...iatek.com>,
        YT Shen <yt.shen@...iatek.com>,
        Daoyuan Huang <daoyuan.huang@...iatek.com>,
        Damon Chu <damon.chu@...iatek.com>,
        Josh-YC Liu <josh-yc.liu@...iatek.com>,
        Glory Hung <glory.hung@...iatek.com>,
        Jiaguang Zhang <jiaguang.zhang@...iatek.com>,
        Dennis-YC Hsieh <dennis-yc.hsieh@...iatek.com>,
        Monica Wang <monica.wang@...iatek.com>
Subject: Re: [PATCH v13 0/4] Mediatek MT8173 CMDQ support

On Thu, Aug 25, 2016 at 7:07 PM, Horng-Shyang Liao <hs.liao@...iatek.com> wrote:
> Hi Matthias,
>
> On Wed, 2016-08-24 at 13:00 +0200, Matthias Brugger wrote:
>> On 24/08/16 05:27, HS Liao wrote:
> [...]
>> > Changes since v12:
>> >  - remove mediatek,gce from device tree
>>
>> Why? The binding got accepted by Rob.
>
> We can get cmdq dev from mailbox controller,
> so we don't need mediatek,gce anymore.
>
>> >
>> > Best regards,
>> > HS Liao
>> >
>> > HS Liao (4):
>> >   dt-bindings: soc: Add documentation for the MediaTek GCE unit
>> >   CMDQ: Mediatek CMDQ driver
>> >   arm64: dts: mt8173: Add GCE node
>> >   CMDQ: save more energy in idle
>> >
>> >  .../devicetree/bindings/soc/mediatek/gce.txt       |  44 +
>> >  arch/arm64/boot/dts/mediatek/mt8173.dtsi           |  10 +
>> >  drivers/soc/mediatek/Kconfig                       |  11 +
>> >  drivers/soc/mediatek/Makefile                      |   1 +
>> >  drivers/soc/mediatek/mtk-cmdq.c                    | 983 +++++++++++++++++++++
>>
>> The driver uses the mailbox framework, so it should live in the
>> drivers/mailbox folder.
>
> As you know, the maximum number of gce threads is 16.
> However, we plan to support more clients in the future,
> and they may need to use more than 16 gce threads.
>
> For this issue, our plan is to let multiple clients share the same gce
> thread; i.e. we will acquire gce thread for client dynamically by
> internal policy in cmdq driver.
> Unfortunately. mailbox channel has exclusive feature.
> Quote from comment of mbox_request_channel().
> "The channel is exclusively allocated and can't be used by another
> client before the owner calls mbox_free_channel."
> Therefore, we plan to remove mailbox framework from cmdq driver in the
> future.
>
Platforms that need shared access to a channel, implement a 'server'
driver that serialise (which is needed still) the access to common
channel. If you think you don't need mutual exclusion and don't care
about replies, simply share the mailbox handle among different
clients.