linux-kernel - Re: [PATCH v5 12/20] memory: mtk-smi: Add gals support

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Message-ID: <CAE=gft5BS=yDQV48V1a=n8U1YyAQuQ+vxg1bFy1HFJXmvXE_gw@mail.gmail.com>
Date:   Wed, 30 Jan 2019 10:30:55 -0800
From:   Evan Green <evgreen@...omium.org>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        Will Deacon <will.deacon@....com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, Arnd Bergmann <arnd@...db.de>,
        yingjoe.chen@...iatek.com, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>
Subject: Re: [PATCH v5 12/20] memory: mtk-smi: Add gals support

On Mon, Dec 31, 2018 at 7:58 PM Yong Wu <yong.wu@...iatek.com> wrote:
>
> In some SoCs like mt8183, SMI add GALS(Global Async Local Sync) module
> which can help synchronize for the modules in different clock frequency.
> It can be seen as a "asynchronous fifo". This is a example diagram:
>
>             M4U
>              |
>          ----------
>          |        |
>      gals0-rx   gals1-rx
>          |        |
>          |        |
>      gals0-tx   gals1-tx
>          |        |
>         ------------
>          SMI Common
>         ------------
>              |
>   +-----+--------+-----+- ...
>   |     |        |     |
>   |  gals-rx  gals-rx  |
>   |     |        |     |
>   |     |        |     |
>   |  gals-tx  gals-tx  |
>   |     |        |     |
> larb1 larb2   larb3  larb4
>
> GALS only help transfer the command/data while it doesn't have the
> configuring register, thus it has the special "smi" clock and doesn't
> have the "apb" clock. From the diagram above, we add "gals0" and
> "gals1" clocks for smi-common and add a "gals" clock for smi-larb.
>
> This patch adds gals clock supporting in the SMI. Note that some larbs
> may still don't have the "gals" clock like larb1 and larb4 above.
>
> This is also a preparing patch for mt8183 which has GALS.
>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>

So really from a software perspective the gals are just a couple of
extra clocks that need to be turned on for certain larbs. Seems fine
to me.

Reviewed-by: Evan Green <evgreen@...omium.org>