RE: [RFC 2/2] pci-expender-bus:Add pcie-root-port to pxb-pcie under arm.

[miaoyubo]

> -----Original Message-----
> From: Daniel P. Berrangé [mailto:address@hidden]
> Sent: Friday, February 14, 2020 6:25 PM
> To: miaoyubo <address@hidden>
> Cc: address@hidden; address@hidden;
> address@hidden; address@hidden; Xiexiangyou
> <address@hidden>; address@hidden
> Subject: Re: [RFC 2/2] pci-expender-bus:Add pcie-root-port to pxb-pcie under
> arm.
> 
> On Fri, Feb 14, 2020 at 07:25:43AM +0000, miaoyubo wrote:
> >
> > > -----Original Message-----
> > > From: Daniel P. Berrangé [mailto:address@hidden]
> > > Sent: Thursday, February 13, 2020 9:52 PM
> > > To: miaoyubo <address@hidden>
> > > Cc: address@hidden; address@hidden;
> > > address@hidden; address@hidden; Xiexiangyou
> > > <address@hidden>; address@hidden
> > > Subject: Re: [RFC 2/2] pci-expender-bus:Add pcie-root-port to
> > > pxb-pcie under arm.
> > >
> > > On Thu, Feb 13, 2020 at 03:49:52PM +0800, Yubo Miao wrote:
> > > > From: miaoyubo <address@hidden>
> > > >
> > > > Since devices could not directly plugged into pxb-pcie, under arm,
> > > > one pcie-root port is plugged into pxb-pcie. Due to the bus for
> > > > each pxb-pcie is defined as 2 in acpi dsdt tables(one for
> > > > pxb-pcie, one for pcie-root-port), only one device could be plugged into
> one pxb-pcie.
> > >
> > > What is the cause of this arm specific requirement for pxb-pcie and
> > > more importantly can be fix it so that we don't need this patch ?
> > > I think it is highly undesirable to have such a per-arch difference
> > > in configuration of the pxb-pcie device. It means any mgmt app which
> > > already supports pxb-pcie will be broken and need to special case arm.
> > >
> >
> > Thanks for your reply, Without this patch, the pxb-pcie is also
> > useable, however, one extra pcie-root-port or pci-bridge or something
> > else need to be defined by mgmt. app. This patch will could be abandoned.
> 
> That's not really answering my question. IIUC, this pxb-pcie device works fine
> on x86_64, and I want to know why it doesn't work on arm ?
> Requiring different setups by the mgmt apps is not at all nice because it will
> inevitably lead to broken arm setups. x86_64 gets far more testing & usage,
> developers won't realize arm is different.
> 
>

Thanks for replying. Currently, on x86_64, pxb-pcie devices is presented in 
acpi tables but on arm, It is not, only one main host bridge is presented for 
arm in acpi dsdt tables. That's why pxb-pcie works on x86_64 but doesn't work 
on arm. The patch 1/2 do the work to present and allocate resources for 
pxb-pcie in arm.
For x86_64, if one device is going to be plugged into pxb-pcie, one extra 
pcie-root-port or pci-bridge have to be defined and plugged on pxb-pcie, then 
the device is plugged on the pcie-root-port or pci-bridge.
This patch 2/2 just auto defined one pcie-root-port for arm. If this patch 
abandoned, the usage of pxb-pcie would be the same with x86_64, therefore, to 
keep the same step for x86 and arm, this patch 2/2 could be abandonded.

 
> 
> Regards,
> Daniel
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Regards,
Miao