Re: Query regarding the use of pcie-designware-plat.c file

[Vidya Sagar]

Given Rob's latest reply, I think Jon's patch addressed the issue in the 
correct way. And IIUC, I think this is how it should be for all Synopsys 
DesignWare implementations unless the implementation really claims that 
it can even work with the generic pcie-designware-plat.c file, otherwise 
it shouldn't contain 'snps,dw-pcie' compatibility string.
IMHO, the addition of 'snps,dw-pcie' along with the respective platform 
specific compatibility string should be strictly restricted.
I think this thread is considered to be concluded at this point.

Thanks,
Vidya Sagar

On 6/16/2021 1:24 PM, Jon Hunter wrote:
> External email: Use caution opening links or attachments
>
>
> On 15/06/2021 20:42, Bjorn Helgaas wrote:
> > On Wed, Jun 09, 2021 at 05:54:38PM +0100, Jon Hunter wrote:
> > > On 09/06/2021 17:30, Bjorn Helgaas wrote:
> > > > On Wed, Jun 09, 2021 at 12:52:37AM +0530, Vidya Sagar wrote:
> > > > > Hi,
> > > > > I would like to know what is the use of pcie-designware-plat.c file. This
> > > > > looks like a skeleton file and can't really work with any specific hardware
> > > > > as such.
> > > > > Some context for this mail thread is, if the config CONFIG_PCIE_DW_PLAT is
> > > > > enabled in a system where a Synopsys DesignWare IP based PCIe controller is
> > > > > present and its configuration is enabled (Ex:- Tegra194 system with
> > > > > CONFIG_PCIE_TEGRA194_HOST enabled), then, it can so happen that the probe of
> > > > > pcie-designware-plat.c called first (because all DWC based PCIe controller
> > > > > nodes have "snps,dw-pcie" compatibility string) and can crash the system.
> > > >
> > > > What's the crash?  If a device claims to be compatible with
> > > > "snps,dw-pcie" and pcie-designware-plat.c claims to know how to
> > > > operate "snps,dw-pcie" devices, it seems like something is wrong.
> > > >
> > > > "snps,dw-pcie" is a generic device type, so pcie-designware-plat.c
> > > > might not know how to operate device-specific details of some of those
> > > > devices, but basic functionality should work and it certainly
> > > > shouldn't crash.
> > >
> > > It is not really a crash but a hang when trying to access the hardware
> > > before it has been properly initialised.
> >
> > This doesn't really answer my question.
> >
> > If the hardware claims to be compatible with "snps,dw-pcie" and a
> > driver knows how to operate "snps,dw-pcie" devices, it should work.
> >
> > If the hardware requires initialization that is not part of the
> > "snps,dw-pcie" programming model, it should not claim to be compatible
> > with "snps,dw-pcie".  Or, if pcie-designware-plat.c is missing some
> > init that *is* part of the programming model, maybe it needs to be
> > enhanced?
>
> Right and this is exactly why I removed the compatible string
> "snps,dw-pcie" for Tegra194 because it is clear that this does not work
> and hence not compatible.
>
> Sagar is purely trying to understand if this is case of other devices as
> well or just Tegra194.
>
> Jon
>
> --
> nvpublic