[PATCH v1] PCI: imx6: Fix i.MX6Q/DL boot hang by separating PHY power and reference clock control

Tue Jul 7 01:55:38 PDT 2026

On 07.07.26 05:03, Hongxing Zhu (OSS) wrote:
>> -----Original Message-----
>> From: Soeren Moch <smoch at web.de>
>> Sent: Monday, July 6, 2026 10:09 PM
>> To: Hongxing Zhu (OSS) <hongxing.zhu at oss.nxp.com>; Frank Li
>> <frank.li at nxp.com>; l.stach at pengutronix.de; lpieralisi at kernel.org;
>> kwilczynski at kernel.org; mani at kernel.org; robh at kernel.org;
>> bhelgaas at google.com; s.hauer at pengutronix.de; kernel at pengutronix.de;
>> festevam at gmail.com
>> Cc: linux-pci at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
>> imx at lists.linux.dev; linux-kernel at vger.kernel.org; Hongxing Zhu
>> <hongxing.zhu at nxp.com>
>> Subject: Re: [PATCH v1] PCI: imx6: Fix i.MX6Q/DL boot hang by separating PHY
>> power and reference clock control
>>
>>
>>
>> On 06.07.26 05:06, hongxing.zhu at oss.nxp.com wrote:
>>> From: Richard Zhu <hongxing.zhu at nxp.com>
>>>
>>> Commit 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling
>>> regulators") introduced a boot hang on i.MX6Q/DL variants by changing
>>> the initialization sequence.
>>>
>>> The issue stems from coupling PHY power (TEST_PD) and reference clock
>>> (REF_CLK_EN) control in imx6q_pcie_enable_ref_clk(). When these are
>>> managed together, the timing between PHY power-up and reference clock
>>> enablement cannot be properly controlled, leading to initialization
>>> failures.
>>>
>>> Fix this by separating the two concerns:
>>>
>>> - Move PHY power control (TEST_PD) to imx6q_pcie_core_reset() where it
>>>     logically belongs with reset operations. This ensures PHY power state
>>>     is managed as part of the core reset sequence.
>>>
>>> - Update imx6qp_pcie_core_reset() to call imx6q_pcie_core_reset() for
>>>     shared PHY power management, avoiding code duplication.
>>>
>>> - Make imx6q_pcie_enable_ref_clk() responsible only for reference clock
>>>     (REF_CLK_EN) control, simplifying its purpose.
>>>
>>> - Remove the 10us delay workaround from imx6q_pcie_enable_ref_clk() as
>>>     proper sequencing is now handled by the core_reset functions.
>>>
>>> This refactoring ensures PHY power is controlled during reset
>>> operations, fixing the boot hang while improving code maintainability.
>>>
>>> Fixes: 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling
>>> regulators")
>>> Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
>> With this patch on top of v7.2-rc2 I see everything booting, lspci shows the
>> root complex, but no PCIe device behind it.
>> Tested on a i.MX6Q based tbs2910 board.
>>
>> For me it is not clear whether this fail to detect PCIe devices is related to the
>> patches in question, the reset timing, or something else. Needs further
>> investigation.
> Thanks for your kindly help to tests.
> Did you ever encounter the boot failure without this patch based on v7.2-rc1
> or later?
Have not tested this. Unfortunately currently I have no access to my 
tbs2910 test board.
I used a production system for this test here, but this is very 
difficult to recover
from boot hangs.
>
> After applied this patch, my i.MX6Q Sabresd board can boot up successfully.
> And the endpoint device can be detected as well.
>
> My Local commits:
> ad5939d49b268 (HEAD -> v7.2-rc2_pcie) PCI: imx6: Add runtime PM support for i.MX95
> db7b15f198125 PCI: imx6: Update MPLLB bandwidth for i.MX95 PCIe Gen3 stability
> a26735515c076 PCI: imx6: Fix i.MX6Q/DL boot hang by separating PHY power and reference clock control
> d617eadf52a46 PCI: dwc: Add force_l2 flag for platforms requiring L2 entry without D3cold
> 8cdeaa50eae8d (tag: v7.2-rc2) Linux 7.2-rc2

My commits (v7.2-rc2 plus my patch to enable MSIs for the endpoint plus 
this patch discussed here):
8cdeaa50eae8 Linux 7.2-rc2
b62414d07e24 PCI: imx6: Keep Root Port MSI capability also for i.MX6Q
e8176c6a27ed PCI: imx6: Fix i.MX6Q/DL boot hang by separating PHY power 
and reference clock control

I'm not sure what your other mentioned patches are.
>
> Kernel logs:
> Starting kernel ...
>
> [    0.000000] Booting Linux on physical CPU 0x0
> [    0.000000] Linux version 7.2.0-rc2-00004-gad5939d49b26 (nxa08258 at shlinux89) (arm-poky-linux-gnueabi-gcc (GCC) 15.2.0, GNU ld (GNU Binutils) 2.45.0.20250908) #38 SMP Tue Jul  7 02:36:46 UTC 2026
> ...
> root at imx6qpdlsolox:~# lspci
> 00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)
> 01:00.0 Ethernet controller: Intel Corporation 82574L Gigabit Network Connection
on linux-7.2-rc2 plus patches (see above):
root at matrix2:~# lspci
00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)

on linux-7.0 (not tested on 7.1):
root at matrix2:~# lspci
00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)
01:00.0 Multimedia controller: Philips Semiconductors SAA7160 (rev 02)

I guess the new power-on/reset timing is not sufficient to init the 
endpoint in time.
Did you reduce the time from powering up the PCIe slot to release of PERST#?
There is a power switch on the tbs2910 board for the PCIe slot, not sure if
this is available also on SabreSD.

Best regards,
Soeren
> Best Regards
> Richard Zhu
>> Regards,
>> Soeren