linux-kernel - Re: [PATCH v9 4/4] PCI: dwc: Support ECAM mechanism by enabling iATU 'CFG Shift Feature'

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Message-ID: <cabf4c20-095b-4579-adc1-146a566b19b9@oss.qualcomm.com>
Date: Fri, 28 Nov 2025 19:14:54 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: Manivannan Sadhasivam <mani@...nel.org>,
        Jingoo Han
 <jingoohan1@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Alim Akhtar
 <alim.akhtar@...sung.com>,
        Jonathan Chocron <jonnyc@...zon.com>, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v9 4/4] PCI: dwc: Support ECAM mechanism by enabling iATU
 'CFG Shift Feature'



On 11/28/2025 2:07 PM, Maciej W. Rozycki wrote:
> On Fri, 28 Nov 2025, Krishna Chaitanya Chundru wrote:
>
>>>> Designware databook r5.20a, sec 3.10.10.3 documents the 'CFG Shift
>>>> Feature'
>>>> of the internal Address Translation Unit (iATU). When this feature is
>>>> enabled, it shifts/maps the BDF contained in the bits [27:12] of the
>>>> target
>>>> address in MEM TLP to become BDF of the CFG TLP. This essentially
>>>> implements the Enhanced Configuration Address Mapping (ECAM) mechanism as
>>>> defined in PCIe r6.0, sec 7.2.2.
>>>    So this broke a parallel port on my HiFive Unmatched machine (a SiFive
>>> FU740-C000 based system), the driver no longer registers the device, no
>>> /dev/parport0 anymore.
>> Hi Maciej, can you share us lspci -vvv o/p with working & non working case and
>> also can you point us parport driver. - Krishna Chaitanya.
>   I'm not sure what you mean as to the parport driver; it's standard stuff:
>
> $ zgrep PARPORT /proc/config.gz
> CONFIG_PARPORT=y
> CONFIG_PARPORT_PC=y
> # CONFIG_PARPORT_SERIAL is not set
> CONFIG_PARPORT_PC_FIFO=y
> CONFIG_PARPORT_1284=y
> # CONFIG_PATA_PARPORT is not set
> # CONFIG_I2C_PARPORT is not set
> # CONFIG_USB_SERIAL_MOS7715_PARPORT is not set
> $
>
> I've attached output from `lspci -xxxx' so that you can decode it yourself
> however you need, though I fail to see anything standing out there.
>
>   If you can't figure out what's going on here, then I'll try to poke at
> the driver to see what exactly it is that causes it to fail there, but I'm
> a little constrained on the resources and completely unfamiliar with the
> ECAM feature (and the lack of documentation for the DW IP does not help).
>
>   I have no slightest idea why it should cause a regression such as this,
> it seems totally unrelated.  Yet it's 100% reproducible.  Could this be
> because it's the only device in the system that actually uses PCI/e port
> I/O?
Hi Maciej, Can you try attached patch and let me know if that is helping 
you or not. - Krishna Chaitanya.
> # cat /proc/ioports
> 00000000-0000ffff : pcie@...000000
>    00001000-00002fff : PCI Bus 0000:01
>      00001000-00002fff : PCI Bus 0000:02
>        00001000-00002fff : PCI Bus 0000:05
>          00001000-00002fff : PCI Bus 0000:06
>            00001000-00001fff : PCI Bus 0000:07
>            00001000-00001007 : 0000:07:00.0
>            00001000-00001002 : parport0
>            00001003-00001007 : parport0
>            00001008-0000100b : 0000:07:00.0
>            00001008-0000100a : parport0
>            00002000-00002fff : PCI Bus 0000:08
>            00002000-00002fff : PCI Bus 0000:09
>            00002000-000020ff : 0000:09:01.0
>            00002100-0000217f : 0000:09:02.0
> #
>
> (Hmm, indentation does not appear correct to me for buses below 0000:07.)
>
>    Maciej

View attachment "0001-PCI-qcom-Enable-iATU-mapping-for-memory-IO-regions.patch" of type "text/plain" (4676 bytes)