On Thu, Mar 30, 2017 at 4:42 PM, Tim Harvey [off-list ref] wrote:

On Fri, Apr 15, 2016 at 1:21 AM, Lucas Stach [off-list ref] wrote:

quoted

Am Donnerstag, den 14.04.2016, 08:13 -0700 schrieb Tim Harvey:

quoted

On Mon, Nov 30, 2015 at 9:00 AM, Lucas Stach [off-list ref] wrote:

quoted

This has been stable on i.MX6 for a good while now and there is no
reason to keep it disabled, as it allows to allocate non-shared
IRQs if several PCIe devices are connected to a single host.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
---
 arch/arm/configs/imx_v6_v7_defconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/configs/imx_v6_v7_defconfig b/arch/arm/configs/imx_v6_v7_defconfig
index 4187f69f6630..e2ce60d00e8a 100644
--- a/arch/arm/configs/imx_v6_v7_defconfig
+++ b/arch/arm/configs/imx_v6_v7_defconfig

@@ -45,6 +45,7 @@ CONFIG_SOC_IMX7D=y
 CONFIG_SOC_LS1021A=y
 CONFIG_SOC_VF610=y
 CONFIG_PCI=y
+CONFIG_PCI_MSI=y
 CONFIG_PCI_IMX6=y
 CONFIG_SMP=y
 CONFIG_PREEMPT_VOLUNTARY=y
--

2.6.2


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Lucas,

Any thoughts on why enabling MSI on IMX6 breaks legacy interrupts?

Again, many PCI devices/drivers don't support MSI and thus enabling
MSI as this patch does makes this config break many PCI devices on
IMX6.

I have found that MSI does indeed work on the IMX6 for cards/drivers
that use MSI, but for those that don't the legacy interrupts never
fire regardless of going through a bridge or directly hanging off the
IMX6. I assume you can confirm this on your boards/devices as well?

No, this seems to be an errata in the DW PCIe core. The manual states
that legacy IRQs and MSIs can't be used together, but I thought this
only applies to the EP part of the core.

We can probably fix the simple configuration by not enabling MSI support
until someone actually requests to set up an MSI IRQ, so both IRQ types
work when only one EP is connected.
I don't have any idea yet how to fix setups with a PCIe switch where
some connected EPs might like to use MSIs while some others can't use
them.

Regards,
Lucas

Lucas,

I feel a bit dumb here for forgetting about this issue and letting it
drop, but I've just spent a day debugging an issue with the ath9k
wireless driver only to realize it was that the ath9k card and/or
driver doesn't support MSI interrupts and thus no longer work on
mainline kernels that have MSI enabled. To be honest I'm not sure how
many PCIe devices out there can't support MSI because of hardware
limitations vs drivers that simply have not implemented it.

To make matters worse 3ee803641e76bea76ec730c80dcc64739a9919ff makes
it such that you can't disable MSI on the IMX6.

Is there some fix you can think of to make the IMX6 PCIe host
controller raise an interrupt for cards/drivers that use legacy irq's?
If not, then we need to allow MSI to be disabled for IMX6 and default
it to disabled for compatibility.

Joao / Jingoo,

(Adding linux-pci to the list to pick up maintainers of other DWC PCIe
core drivers)

Is Luca's statement that 'legacy IRQs and MSIs can't be used together'
true in general for the DW PCIe core? If any of the host controllers
using this core can't support both legacy and MSI irqs together I
still believe we shouldn't enable/require MSI as it breaks any
card/driver that only supports legacy interrupts (such as ath9k).

Regards,

Tim