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

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Date:   Tue, 20 Oct 2020 13:37:25 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Z.q. Hou" <zhiqiang.hou@....com>
CC:     Rob Herring <robh@...nel.org>,
        Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Michael Walle <michael@...le.cc>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH] PCI: dwc: Added link up check in map_bus of
 dw_child_pcie_ops

Hi Lorenzo,

On 19/10/20 9:43 pm, Lorenzo Pieralisi wrote:
> On Mon, Oct 12, 2020 at 04:41:11AM +0000, Z.q. Hou wrote:
> 
> [...]
> 
>>>>> Yeah, I don't see any registers in the DRA7x PCIe wrapper for
>>>>> disabling error forwarding.
>>>>
>>>> It's a DWC port logic register AFAICT, but perhaps not present in all
>>> versions.
>>>
>>> Okay. I see there's a register PCIECTRL_PL_AXIS_SLV_ERR_RESP which has a
>>> reset value of 0.
>>>
>>> It has four bit-fields, RESET_TIMEOUT_ERR_MAP, NO_VID_ERR_MAP,
>>> DBI_ERR_MAP and SLAVE_ERR_MAP. I'm not seeing any difference in
>>> behavior if I set all these bits. Maybe it requires platform support too. I'll
>>> check this with our design team.
>>
>> In DWC v4.40a databook, there is a bit AMBA_ERROR_RESPONSE_GLOBAL
>> which controls if enable the error forwarding. The *MAP bits only
>> determine which error (SLVERR or DECERR) will be forwarded to AXI/AHB
>> bus.
> 
> I have not seen a follow-up to this but I would like to, still keen
> on avoiding this patch if possible - if this is port logic it should
> be common across controllers implementations I assume.
> 
> Gustavo, Kishon ?

Atleast in the TI DRA7 TRM, I could see only
PCIECTRL_PL_AXIS_SLV_ERR_RESP and PCIECTRL_PL_AXIS_SLV_TIMEOUT register
but no global error response bit. I'd have expected configuring
SLV_ERR_RESP would have disabled error forwarding, but I don't see any
change in behavior if I modify the value of PCIECTRL_PL_AXIS_SLV_ERR_RESP.

TI PCIe controller in DRA7 is not directly connected to AXI/AHB but
there is an intermediary bridge. So I suspect there is some issue on how
the controller is integrated in TI platform. Since the board hangs, I
couldn't get lot of visibility of controller state.

Thanks
Kishon