linux-kernel - Re: [PATCH] dt-bindings: imx: update scu resource id headfile

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Date:   Wed, 20 Feb 2019 11:52:49 +0100
From:   Marco Felsch <m.felsch@...gutronix.de>
To:     Aisheng Dong <aisheng.dong@....com>
Cc:     Anson Huang <anson.huang@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH] dt-bindings: imx: update scu resource id headfile

Hi Aisheng,

On 19-02-20 09:49, Aisheng Dong wrote:
> > From: Marco Felsch [mailto:m.felsch@...gutronix.de]
> > Sent: Wednesday, February 20, 2019 4:17 PM
> > On 19-02-20 03:38, Aisheng Dong wrote:
> > > [...]
> > >
> > > > > I don't like droping some ID's (e.g. IMX_SC_R_DC_0_CAPTURE0) by
> > > > > mark them as unused or even worse give them a other meaning. IMHO
> > > > > the scu-api should be stable since day 1 and the ID's should only be
> > extended.
> > > > > Marking ID's as deprecated is much better than moving them around.
> > > >
> > > > I agree the SCU APIs should be stable since day 1 and the ID should
> > > > ONLY be extended, but that is the best cases, the reality is, there
> > > > are different SoCs/Revision, some revisions may remove the resources
> > > > ID defined in pre-coded SCU firmware, like the
> > > > IMX_SC_R_DC_0_CAPTURE0 etc., so SCU APIs removes them after real
> > > > silicon arrived, now latest SCU firmware marks them as UNUSED, they
> > > > could be replaced by some other new resources in later new SoC, I am
> > > > NOT sure, but if it happens, this resource ID table should be
> > > > updated anyway, leaving the out-of-date resource ID table there will have
> > issues, since it is NOT sync with SCU firmware.
> > > >
> > > > So how to resolve such issue? We hope the SCU firmware should be
> > > > stable since day 1, but the truth is NOT, could be still some
> > > > updates but NOT very often. And I believe the updates will NOT break old
> > kernel version.
> > 
> > Hi Anson,
> > 
> > Please don't mix the dt-bindings and the kernel related stuff.
> > Unfortunately the bindings are within the kernel repo which in fact is great for
> > us kernel developer but the bindings are also used in other projects such as
> > barebox or other kernels (don't know the BSD guys). So you can't ensure that
> > your change will break something. Please keep that in mind.
> > 
> > IMHO solving that issue should be done by the scu firmware. I tought the scu is
> > a cortex-m4 with a bunch of embedded flash and ram (I don't know that much
> > about the scu since it is closed/black-boxed). Why do you don't use a
> > translation table within the scu? As I said earlier I don't like the redefinition of
> > ID's since they are now part of the dt-bindings.
> > The bindings can store up to 32bit values which is a large number ;) IMHO
> > wasting some ID's in favour of stability is a better solution.
> > 
> 
> As far as I know, those remove resource IDs are pre-defined and has never been used
> and won't be used anymore by SC firmware. (Anson can double check it)
> So I think it's safe to remove them or mark them as deprecated.

I think marking them as deprecated by a commentar is better than
redefining bits to be unused. As I said the bindings not only linux
related they are used in other projects too.

> 
> Personally I may prefer to remove them as they never worked to avoid confusing,
> especially at this early stage for mx8.

So why they are there if they never worked? Wouldn't it a better
approach to start with a basic and working ID file and extend this
rather than adding id's because maybe the will work.. Sorry but this
seems wrong to me too.
I know the approach from driver development, adding a driver specific
*_reg.h file and later figuring out that those bits won't work as
aspected. As I said this will be driver and only linux related so we can
change them as many times as we want. But in your case we are talking
about dt-bindings and this approach won't work.

Regards,
Marco

> 
> Regards
> Dong Aisheng
> 

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