Re: [PATCH v2] PCI: imx6: Keep Root Port MSI capability also for i.MX6Q

[Soeren Moch <smoch@web.de>]

On 17.07.26 00:27, Bjorn Helgaas wrote:
> On Thu, Jul 16, 2026 at 11:40:54PM +0200, Soeren Moch wrote:
>> On the NXP i.MX6Q chipset MSIs from the endpoints won't be received by
>> the iMSI-RX MSI controller if the Root Port MSI capability is disabled.
>>
>> Even though the Root Port MSIs won't be received by the iMSI-RX controller
>> due to design, this chipset has some weird hardware bug that prevents
>> the endpoint MSIs from reaching when the Root Port MSI capability is
>> disabled.
>>
>> Hence, always keep the Root Port MSI capability for this chipset.
>>
>> Note that by keeping Root Port MSI capability, Root Port MSIs such as AER,
>> PME and others won't be received by default. So users need to use
>> workarounds such as passing 'pcie_pme=nomsi' cmdline param.
> I'd like to align the subject a little more with 3a4e8302e72f and
> avoid repeating the ".. from reaching when the Root Port MSI ..." part
> of the commit log, which seems to be missing a word.  So I propose the
> following (if you think it's accurate):
Your proposed new patch subject and commit message is totally fine for me.

Thanks,
Soeren
>
>    PCI: imx6: Keep i.MX6Q Root Port MSI capability with iMSI-RX to work around hardware bug
>
>    On some NXP chipsets, disabling Root Port MSI/MSI-X Capabilities blocks
>    MSIs originating from Endpoints from reaching the iMSI-RX controller.
>
>    To address this hardware bug, 3a4e8302e72f ("PCI: imx6: Keep Root Port MSI
>    capability with iMSI-RX to work around hardware bug") preserves Root Port
>    MSI and MSI-X Capabilities on i.MX7D, i.MX8MM, and i.MX8MQ when iMSI-RX is
>    in use.
>
>    The same applies to i.MX6Q, so preserve Root Port MSI/MSI-X Capabilities
>    there as well.
>
>    Note that preserving these Capabilities means Root Port-originated MSIs
>    such as AER and PME won't be received due to separate hardware limitations.
>    Users may need to use workarounds such as passing the 'pcie_pme=nomsi'
>    command-line parameter.
>
> Also, we need to resolve the Sashiko question about whether IMX6QP and
> IMX6SX also need this.  NXP folks, can you verify?
>
>> Fixes: f5cd8a929c825 ("PCI: dwc: Remove MSI/MSIX capability for Root Port if iMSI-RX is used as MSI controller")
>> Cc: <stable@vger.kernel.org> # 7.0+
>> Signed-off-by: Soeren Moch <smoch@web.de>
>> Acked-by: Richard Zhu <hongxing.zhu@nxp.com>
>> Reviewed-by: Frank Li <Frank.Li@nxp.com>
>> Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
>> ---
>> Cc: Manivannan Sadhasivam <mani@kernel.org>
>> Cc: Richard Zhu <hongxing.zhu@nxp.com>
>> Cc: Lucas Stach <l.stach@pengutronix.de>
>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: Frank Li <Frank.Li@nxp.com>
>> Cc: Fabio Estevam <festevam@gmail.com>
>> Cc: linux-pci@vger.kernel.org
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: imx@lists.linux.dev
>> Cc: linux-kernel@vger.kernel.org
>>
>> This patch is similar to
>> 3a4e8302e72f ("PCI: imx6: Keep Root Port MSI capability with iMSI-RX to work around hardware bug")
>>
>> Tested on a tbs2910 board [1]
>> [1] arch/arm/boot/dts/nxp/imx/imx6q-tbs2910.dts
>>
>> changes in v2:
>> - collect a-b and r-b tags
>> - use correct fixes tag (Manivannan)
>>    (reference commit that introduced the bug, not the incomplete fix)
>>
>> Since this is a fix for a regression in linux-7.0+, can this still be merged for 7.2-rcS ?
>> ---
>>   drivers/pci/controller/dwc/pci-imx6.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
>> index 98e1db751132..8130cf93c2bb 100644
>> --- a/drivers/pci/controller/dwc/pci-imx6.c
>> +++ b/drivers/pci/controller/dwc/pci-imx6.c
>> @@ -1995,7 +1995,8 @@ static const struct imx_pcie_drvdata drvdata[] = {
>>   		.flags = IMX_PCIE_FLAG_IMX_PHY |
>>   			 IMX_PCIE_FLAG_SPEED_CHANGE_WORKAROUND |
>>   			 IMX_PCIE_FLAG_BROKEN_SUSPEND |
>> -			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
>> +			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND |
>> +			 IMX_PCIE_FLAG_KEEP_MSI_CAP,
>>   		.dbi_length = 0x200,
>>   		.gpr = "fsl,imx6q-iomuxc-gpr",
>>   		.ltssm_off = IOMUXC_GPR12,
>> -- 
>> 2.43.0
>>