linux-kernel - Re: [PATCH 1/4] dt-bindings: reset: Add binding for Sophgo CV1800B reset controller

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Message-ID: <ZVTHMsXaPdHiuUOF@xhacker>
Date:   Wed, 15 Nov 2023 21:27:14 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Chao Wei <chao.wei@...hgo.com>,
        Chen Wang <unicorn_wang@...look.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 1/4] dt-bindings: reset: Add binding for Sophgo CV1800B
 reset controller

On Tue, Nov 14, 2023 at 10:12:35PM +0100, Krzysztof Kozlowski wrote:
> On 13/11/2023 01:55, Jisheng Zhang wrote:
> ...
> 
> > diff --git a/include/dt-bindings/reset/sophgo,cv1800b-reset.h b/include/dt-bindings/reset/sophgo,cv1800b-reset.h
> > new file mode 100644
> > index 000000000000..28dda71369b4
> > --- /dev/null
> > +++ b/include/dt-bindings/reset/sophgo,cv1800b-reset.h
> > @@ -0,0 +1,96 @@
> > +/* SPDX-License-Identifier: GPL-2.0 OR MIT */
> > +/*
> > + * Copyright (C) 2023 Sophgo Technology Inc. All rights reserved.
> > + * Copyright (C) 2023 Jisheng Zhang <jszhang@...nel.org>
> > + */
> > +
> > +#ifndef _DT_BINDINGS_CV1800B_RESET_H
> > +#define _DT_BINDINGS_CV1800B_RESET_H
> > +
> > +/*				0-1	*/
> > +#define RST_DDR			2
> > +#define RST_H264C		3
> > +#define RST_JPEG		4
> > +#define RST_H265C		5
> > +#define RST_VIPSYS		6
> > +#define RST_TDMA		7
> > +#define RST_TPU			8
> > +#define RST_TPUSYS		9
> > +/*				10	*/
> 
> Why do you have empty IDs? IDs start at 0 and are incremented by 1.

there's 1:1 mapping between the ID and bit. Some bits are reserved, I.E
no actions at all. Is "ID start at 0 and increment by 1" documented
in some docs? From another side, I also notice some SoCs especially
those which make use of reset-simple driver don't strictly follow
this rule, for example, amlogic,meson-a1-reset.h and so on. What
happened?

And I'd like to ask a question here before cooking 2nd version:
if the HW programming logic is the same as reset-simple, but some
or many bits are reserved, what's the can-be-accepted way to support
the reset controller? Use reset-simple? Obviously if we want the
"ID start at 0 and increment by 1" rule, then we have to write
a custom driver which almost use the reset-simple but with a
customized mapping.

Thanks