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

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

On 11/28/2025 8:47 AM, Maciej W. Rozycki wrote:
> On Tue, 9 Sep 2025, Manivannan Sadhasivam wrote:
>
>> From: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
>>
>> 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've had to bisect it with commit a1978b692a39 ("PCI: dwc: Use custom
> pci_ops for root bus DBI vs ECAM config access") and commit fc2bc2623e3a
> ("Revert "PCI: qcom: Prepare for the DWC ECAM enablement"") applied on top
> and it's affirmative it's this change, i.e. upstream commit 0da48c5b2fa7
> ("PCI: dwc: Support ECAM mechanism by enabling iATU 'CFG Shift Feature'").
>
>   Here's the relevant part of a diff between bootstrap logs:
>
> --- dmesg-good.log	2025-11-28 03:41:18.943097032 +0100
> +++ dmesg-bad.log	2025-11-28 03:47:29.582049781 +0100
> @@ -1,5 +1,5 @@
> -Booting Linux on hartid 3
> -Linux version 6.17.0-rc1-00008-g4660e50cf818-dirty (macro@angie) (riscv64-linux-gnu-gcc (GCC) 13.0.0 20220602 (experimental), GNU ld (GNU Binutils) 2.38.50.20220503) #19 SMP Fri Nov 28 02:37:51 GMT 2025
> +Booting Linux on hartid 1
> +Linux version 6.17.0-rc1-00009-g0da48c5b2fa7-dirty (macro@angie) (riscv64-linux-gnu-gcc (GCC) 13.0.0 20220602 (experimental), GNU ld (GNU Binutils) 2.38.50.20220503) #20 SMP Fri Nov 28 02:43:00 GMT 2025
>   Machine model: SiFive HiFive Unmatched A00
>   SBI specification v0.3 detected
>   SBI implementation ID=0x1 Version=0x9
> @@ -61,7 +61,7 @@
>   EFI services will not be available.
>   smp: Bringing up secondary CPUs ...
>   smp: Brought up 1 node, 4 CPUs
> -Memory: 16383064K/16777216K available (10746K kernel code, 2200K rwdata, 4972K rodata, 537K init, 371K bss, 389448K reserved, 0K cma-reserved)
> +Memory: 16383064K/16777216K available (10746K kernel code, 2200K rwdata, 4972K rodata, 536K init, 371K bss, 389448K reserved, 0K cma-reserved)
>   devtmpfs: initialized
>   clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
>   posixtimers hash table entries: 2048 (order: 3, 32768 bytes, linear)
> @@ -161,6 +161,7 @@
>   fu740-pcie e00000000.pcie:       IO 0x0060080000..0x006008ffff -> 0x0060080000
>   fu740-pcie e00000000.pcie:      MEM 0x0060090000..0x007fffffff -> 0x0060090000
>   fu740-pcie e00000000.pcie:      MEM 0x2000000000..0x3fffffffff -> 0x2000000000
> +fu740-pcie e00000000.pcie: ECAM at [mem 0xdf0000000-0xdffffffff] for [bus 00-ff]
>   fu740-pcie e00000000.pcie: Using 256 MSI vectors
>   fu740-pcie e00000000.pcie: iATU: unroll T, 8 ob, 8 ib, align 4K, limit 4096G
>   fu740-pcie e00000000.pcie: cap_exp at 70
> @@ -655,7 +656,7 @@
>   usb usb1: New USB device found, idVendor=1d6b, idProduct=0002, bcdDevice= 6.17
>   usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
>   usb usb1: Product: xHCI Host Controller
> -usb usb1: Manufacturer: Linux 6.17.0-rc1-00008-g4660e50cf818-dirty xhci-hcd
> +usb usb1: Manufacturer: Linux 6.17.0-rc1-00009-g0da48c5b2fa7-dirty xhci-hcd
>   usb usb1: SerialNumber: 0000:04:00.0
>   hub 1-0:1.0: USB hub found
>   hub 1-0:1.0: 2 ports detected
> @@ -663,7 +664,7 @@
>   usb usb2: New USB device found, idVendor=1d6b, idProduct=0003, bcdDevice= 6.17
>   usb usb2: New USB device strings: Mfr=3, Product=2, SerialNumber=1
>   usb usb2: Product: xHCI Host Controller
> -usb usb2: Manufacturer: Linux 6.17.0-rc1-00008-g4660e50cf818-dirty xhci-hcd
> +usb usb2: Manufacturer: Linux 6.17.0-rc1-00009-g0da48c5b2fa7-dirty xhci-hcd
>   usb usb2: SerialNumber: 0000:04:00.0
>   hub 2-0:1.0: USB hub found
>   hub 2-0:1.0: 2 ports detected
> @@ -735,8 +736,6 @@
>   pcieport 0000:06:01.0: enabling bus mastering
>   parport_pc 0000:07:00.0: enabling device (0000 -> 0001)
>   PCI parallel port detected: 1415:c118, I/O at 0x1000(0x1008), IRQ 35
> -parport0: PC-style at 0x1000 (0x1008), irq 35, using FIFO [PCSPP,TRISTATE,EPP,ECP]
> -lp0: using parport0 (interrupt-driven).
>   parport_pc 0000:07:00.0: vgaarb: pci_notify
>   serial 0000:07:00.3: vgaarb: pci_notify
>   serial 0000:07:00.3: assign IRQ: got 40
>
> and then it goes on with insignificant changes only owing to differences
> in the order of messages produced, the kernel version ID or date stamps.
> As you can see the PCIe parallel port device continues being accessible,
> it's only the driver that doesn't pick up the device anymore.
>
>   I'm stumped as to where it might be coming from.  Any ideas?
>
>    Maciej