linux-kernel - RE: [PATCH] PCI: dwc: Added link up check in map_bus of dw_child_pcie

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Date:   Wed, 21 Oct 2020 08:47:59 +0000
From:   "Z.q. Hou" <zhiqiang.hou@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Richard Zhu <hongxing.zhu@....com>
CC:     Kishon Vijay Abraham I <kishon@...com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "robh@...nel.org" <robh@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>
Subject: RE: [PATCH] PCI: dwc: Added link up check in map_bus of
 dw_child_pcie_ops

Hi Lorenzo and Richard,

> -----Original Message-----
> From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Sent: 2020年10月20日 17:55
> To: Z.q. Hou <zhiqiang.hou@....com>
> Cc: Kishon Vijay Abraham I <kishon@...com>; Bjorn Helgaas
> <helgaas@...nel.org>; linux-kernel@...r.kernel.org;
> linux-pci@...r.kernel.org; robh@...nel.org; bhelgaas@...gle.com;
> gustavo.pimentel@...opsys.com
> Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of
> dw_child_pcie_ops
> 
> On Tue, Oct 20, 2020 at 02:13:13AM +0000, Z.q. Hou wrote:
> 
> [...]
> 
> > > > For NXP Layerscape platforms (the ls1028a and ls2088a are also NXP
> > > Layerscape platform), as the error response to AXI/AHB was enabled,
> > > it will get UR error and trigger SError on AXI bus when it accesses
> > > a non-existent BDF on a link down bus. I'm not clear about how it
> > > happens on dra7xxx and imx6, since they doesn't enable the error
> response to AXI/AHB.
> > >
> > > That's exactly the case with DRA7xx as the error response is enabled
> > > by default in the platform integration.
> >
> > Got feedback from the imx6 owner that imx6 like the dra7xx has the
> > error response enabled by default.  Now it's clear that the problem on
> > all these platforms is the same.
> 
> On IMX6, enabled by default and read-only ? Or it can be changed ? 

The AXI/AHB Bridge Slave Error Response Register is a common register of DWC IP, so I think it should be writeable. Richard, can you help to confirm?

> What's the plan for layerscape on this matter ?

I trend to change it back to the default error response behavior so that won't cause any error on CFG access, and have sent out the patch.
And for the link up check before CFG accesses, in the DWC databoot (4.40a), it requires link up check before generating CFG requests, so need Gustavo help to make sure the reason of this requirement, any potential impact without the link up check.

Thanks,
Zhiqiang
> 
> Lorenzo