linux-kernel - RE: [PATCH v3 1/8] arm64: dts: ls1028a: Add PCIe EP nodes

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Date:   Wed, 13 Apr 2022 18:38:54 +0000
From:   Leo Li <leoyang.li@....com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     "Z.Q. Hou" <zhiqiang.hou@....com>, Shawn Guo <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xiaowei Bao <xiaowei.bao@....com>
Subject: RE: [PATCH v3 1/8] arm64: dts: ls1028a: Add PCIe EP nodes



> -----Original Message-----
> From: Vladimir Oltean <olteanv@...il.com>
> Sent: Wednesday, April 13, 2022 1:22 PM
> To: Leo Li <leoyang.li@....com>
> Cc: Z.Q. Hou <zhiqiang.hou@....com>; Shawn Guo
> <shawnguo@...nel.org>; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; Xiaowei Bao <xiaowei.bao@....com>
> Subject: Re: [PATCH v3 1/8] arm64: dts: ls1028a: Add PCIe EP nodes
> 
> On Wed, Apr 13, 2022 at 06:03:37PM +0000, Leo Li wrote:
> > > arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi:631.23-656.5: Warning
> > > (unique_unit_address): /soc/pcie@...0000: duplicate unit-address
> > > (also used in node /soc/pcie-ep@...0000)
> > > arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi:670.23-695.5: Warning
> > > (unique_unit_address): /soc/pcie@...0000: duplicate unit-address
> > > (also used in node /soc/pcie-ep@...0000)
> >
> > This would be a common problem for all the layerscape PCIe controller.
> > The controller can either work in RC mode or EP mode.  The current
> > binding of the controller defined two compatibles, one for RC and one
> > for EP.  Therefore the SoC dtsi will have two nodes with the same unit
> > address one for EP one for RC.  Fixing this probably requires
> > comprehensive updates to the binding which breaks backward
> > compatibility.
> 
> So we have to live with these warnings forever now?
> 
> How are the PCIe controllers configured for RC or EP mode? Via RCW?
> Is dynamic configuration possible?

Yes. It is configured via RCW on reset.  I don't think it can be changed at runtime.

> 
> Can't U-Boot detect the operating mode from the RCW and fix up the
> compatible string in case the controller is in endpoint mode?

I believe the u-boot is already updating the node status to enable the correct one.  But it might be confusing to change the compatible and a bunch of other properties at boot time.

Regards,
Leo