linux-kernel - Re: [PATCH 1/1] arm64: dts: lx2160a: Change PCIe compatible string to fsl,ls2088a-pcie

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Message-ID: <CAL_JsqLzvEpXbTk0XjPuErz2nRaTXX1DP9WG8yshULcVv0bS-Q@mail.gmail.com>
Date: Mon, 12 Aug 2024 11:29:38 -0600
From: Rob Herring <robh@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Conor Dooley <conor@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	"moderated list:ARM/FREESCALE LAYERSCAPE ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>, 
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>, 
	imx@...ts.linux.dev
Subject: Re: [PATCH 1/1] arm64: dts: lx2160a: Change PCIe compatible string to fsl,ls2088a-pcie

On Fri, Aug 9, 2024 at 11:11 AM Frank Li <Frank.li@....com> wrote:
>
> On Fri, Aug 09, 2024 at 04:07:25PM +0100, Conor Dooley wrote:
> > On Thu, Aug 08, 2024 at 12:15:03PM -0400, Frank Li wrote:
> > > On Thu, Aug 08, 2024 at 04:55:14PM +0100, Conor Dooley wrote:
> > > > On Thu, Aug 08, 2024 at 11:51:34AM -0400, Frank Li wrote:
> > > > > On Thu, Aug 08, 2024 at 04:34:32PM +0100, Conor Dooley wrote:
> > > > > > On Thu, Aug 08, 2024 at 11:31:20AM -0400, Frank Li wrote:
> > > > > > > The mass production lx2160 rev2 use designware PCIe Controller. Old Rev1
> > > > > > > which use mobivel PCIe controller was not supported. Although uboot
> > > > > > > fixup can change compatible string fsl,lx2160a-pcie to fsl,ls2088a-pcie
> > > > > > > since 2019, it is quite confused and should correctly reflect hardware
> > > > > > > status in fsl-lx2160a.dtsi.
> > > > > >
> > > > > > This does not begin to explain why removing the soc-specific compatible,
> > > > > > and instead putting the compatible for another soc is the right fix.
> > > > > > Come up with a new compatible for this device, that perhaps falls back
> > > > > > to the ls2088a, but this change doesn't seem right to me.
> > > > >
> > > > > It can't fallback to fsl,ls2088a-pcie if fsl,lx2160a-pcie exist, which are
> > > > > totally imcompatible between fsl,ls2088a-pcie and fsl,lx2160a-pcie.
> > > > >
> > > > > Previous dtb can work just because uboot dynamtic change fsl,lx2160a-pcie
> > > > > to fsl,ls2088a-pcie when boot kernel.
> > > > >
> > > > > fsl,lx2160a-pcie should be removed because Rev1 have not mass productioned.
> > > >
> > > > Please re-read what I wrote. I said to come up with a new compatible for
> > > > this device, not fall back from the existing fsl,lx2160a-pcie to
> > > > fsl,ls2088a-pcie.
> > >
> > > According to my understand, It needn't add new compatible string if nothing
> > > difference. for example, it use fsl,vf610-i2c for all i2c without add
> > > new soc-specific fsl,lx2160-i2c.
> >
> > No, you should have soc-specific compatibles regardless. Just because
> > you got away with it once, doesn't mean I'm not going to complain about
> > it here!
>
> Rob:
>         What's current policy for this? Not only for this one. If new SOC
> appear such as iMX10 (maybe many derived chip i.MX101, i.MX102...), there
> are bunch of IPs, Do we need add fsl,imx10* for everyone, which most part
> is exactly the same as old one and bloat binding doc.

Yes, you do. Do you really know that something in the design hasn't
changed? Have you compared the RTL between the versions? The only way
to deal with quirks without changing the DT everytime is by having
specific compatibles *upfront*.

The "bloat" is never that much because the IP really always changes.
QCom wanted to (and did) use IP version numbers for the same reasons.
Guess what, the IP version number changed on almost every SoC.

The exceptions are really if different SoCs are just different
packaging or fusing.


In this case, I'm inclined to say just match what u-boot creates, but
please make that abundantly clear with a comment in the .dts file and
explain the situation in the commit message. OTOH, just adding a new
"fsl,lx2160a-dw-pcie" compatible with "fsl,ls2088a-pcie" fallback
doesn't hurt, and we can just move on from creating a special case.

Rob