On Wed, Feb 27, 2019 at 2:01 AM Lucas Stach <l.stach@xxxxxxxxxxxxxx> wrote:
>
> Hi Tim,
>
> Am Dienstag, den 26.02.2019, 13:13 -0800 schrieb Tim Harvey:
> > Greetings,
> >
> > I've got a miniPCIe card with a TW6869 8x frame grabber that stopped
> > working on an IMX6 based board with a PLX switch with Linux 4.17 as
> > the driver errors out with 'tw686x 0000:07:00.0: unable to request
> > interrupt' (request_irq() fails). I've found this only happens on
> > boards that have a switch. Note I'm booting with pci=nomsi as well as
> > the IMX6 has a limitation where legacy IRQ's wont fire if MSI irq's
> > are enabled. Strangely I don't see this issue with other cards such
> > as
> > the ath9k with msi disabled.
> >
> > I bisected the issue to 7c5925afbc58c6d6b384e1dc051bb992969bf787
> > 'PCI:
> > dwc: Move MSI IRQs allocation to IRQ domains hierarchical API' which
> > due to continued changes in drivers/pci/dwc can no longer be
> > reverted.
> >
> > Any ideas what happened here? IMX6 PCIe through a bridge always seems
> > not so well tested and very fragile over the past couple of years.
>
> Thanks for the report. Both the DWC PCIe core in general and the i.MX6
> integration have some rough edges, which makes things fall from time to
> time. Having a PCIe bridge in the mix does extend the test space quite
> a bit.
>
> Does the following patch help? I didn't test it yet, but it's based on
> my assumption of what is going wrong with the referenced commit.
>
> Regards,
> Lucas
>
> ----------------------------->8--------------------------------------
>
> From 40b4fc03878a935fa81af226a8e759d4c72a3603 Mon Sep 17 00:00:00 2001
> From: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> Date: Wed, 27 Feb 2019 10:50:20 +0100
> Subject: [PATCH] PCI: dwc: skip MSI init if MSIs have been explicitly disabled
>
> Since 7c5925afbc58 (PCI: dwc: Move MSI IRQs allocation to IRQ domains
> hierarchical API) the MSi init claims one of the controller IRQs as a
> chained IRQ line for the MSI controller. On some designs, like the i.MX6,
> this line is shared with a PCIe legacy IRQ. When the line is claimed for
> the MSI domain, any device trying to use this legacy IRQs will fail to
> request this IRQ line.
>
> As MSI and legacy IRQs are already mutually exclusive on the DWC core,
> as the core won't forward any legacy IRQs once any MSI has been enabled,
> users wishing to use legacy IRQs already need to explictly disable MSI
> support (usually via the pci=nomsi kernel commandline option). To avoid
> any issues with MSI conflicting with legacy IRQs, just skip all of the
> DWC MSI initalization, inclusing the IRQ line claim, when MSI is disabled.
>
> Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> ---
> drivers/pci/controller/dwc/pcie-designware-host.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 29a05759a294..f4a8494f616b 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -433,7 +433,7 @@ int dw_pcie_host_init(struct pcie_port *pp)
> if (ret)
> pci->num_viewport = 2;
>
> - if (IS_ENABLED(CONFIG_PCI_MSI)) {
> + if (IS_ENABLED(CONFIG_PCI_MSI) && pci_msi_enabled()) {
> /*
> * If a specific SoC driver needs to change the
> * default number of vectors, it needs to implement
> --
> 2.20.1
Lucas,
Yes, this patch resolves the issue. Where did this come from? It looks
like it came from back in September but never made it upstream?
I'm a bit baffled why I see this issue pre-patch with 'and' without
pci=nomsi based on this patch? I do see other checks in
imx6_pcie_host_init() and imx6_add_pcie_port() for
IS_ENABLED(CONFIG_PCI_MSI) that do not have an accompanying check of
pci_msi_enabled() to see if its enabled at runtime... are these
problematic as well?
I'm wondering if pci=nosmi is not well tested. I use it because of the
issue where IMX6 can't use MSI and legacy interrupts at the same time
in addition to the fact that MSI shares a single hardware interrupt
while legacy at least has 4 unit interrupts (making it able to be
steered). I'm just not a fan of MSI in the embedded arena where users
have 1 or 2 PCI devices.
Regards,
Tim
