linux-kernel - Re: [linux-sunxi] Re: [PATCH 2/7] dt-bindings: add binding for the Allwinner A64 DE2 bus

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Message-ID: <20180326222258.uxpgj4bk4pg56b7o@rob-hp-laptop>
Date:   Mon, 26 Mar 2018 17:22:58 -0500
From:   Rob Herring <robh@...nel.org>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     jernej.skrabec@...l.net, linux-sunxi@...glegroups.com,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [linux-sunxi] Re: [PATCH 2/7] dt-bindings: add binding for the
 Allwinner A64 DE2 bus

On Thu, Mar 22, 2018 at 02:08:43PM +0800, Icenowy Zheng wrote:
> 
> 
> 于 2018年3月22日 GMT+08:00 上午1:13:42, "Jernej Škrabec" <jernej.skrabec@...l.net> 写到:
> >Hi all,
> >
> >Dne sreda, 21. marec 2018 ob 03:18:13 CET je Icenowy Zheng napisal(a):
> >> 于 2018年3月21日 GMT+08:00 上午2:46:46, Maxime Ripard
> ><maxime.ripard@...tlin.com> 
> >写到:
> >> >On Sat, Mar 17, 2018 at 01:53:49AM +0800, Icenowy Zheng wrote:
> >> >> All the sub-blocks of Allwinner A64 DE2 needs the SRAM C on A64
> >SoC
> >> >
> >> >to
> >> >
> >> >> be claimed, otherwise the whole DE2 space is inaccessible.
> >> >> 
> >> >> Add a device tree binding of the DE2 part as a sub-bus.
> >> >
> >> >Where did you get the info that it was a bus?
> >> 
> >> There's no direct evidence, just some guess.
> >> 
> >> The DE2 is a whole part that is just allocated a memory
> >> space at the user manual, and the SRAM controls the
> >> access to all modules in the DE2.
> >> 
> >> So it might be a bus.
> >> 
> >> Implement it as a bus is a clear representation on A64.
> >
> >Since there is already syscon for same mmio region, we migh as well use
> >it 
> >when loading ccu-sun8i-de2 driver on A64.
> >
> >Other options, like SRAM driver or bus driver, might better represent
> >HW, but 
> 
> I think the device tree should properly represent the HW,
> it's a basic requirment.
> 
> >then we would have two DT nodes covering same mmio region, which I
> >think is 
> >not really acceptable.
> 
> It's acceptable, and DE2 is not the only user of SRAM controller so far.

No, it's not acceptable. Don't create overlapping mmio regions in DT.

> 
> VE will also need a SRAM region to be claimed.
> 
> >
> >Any suggestions?
> >
> >BTW, H6 has same design in this regard.
> >
> >Best regards,
> >Jernej
> --
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