Date:   Wed, 28 Nov 2018 18:56:19 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Leonard Crestez <leonard.crestez@....com>,
        lorenzo.pieralisi@....com, Trent Piepho <tpiepho@...inj.com>,
        Richard Zhu <hongxing.zhu@....com>,
        linux-kernel@...r.kernel.org, jingoohan1@...il.com,
        gustavo.pimentel@...opsys.com, andrew.smirnov@...il.com,
        linux-pci@...r.kernel.org, bhelgaas@...gle.com
Subject: Re: [PATCH v3 2/2] PCI: imx6: limit DBI register length

On 28.11.2018 18:50, Lucas Stach wrote:
> Am Mittwoch, den 28.11.2018, 18:36 +0100 schrieb Stefan Agner:
>> On 28.11.2018 13:19, Stefan Agner wrote:
>> > On 21.11.2018 14:47, Leonard Crestez wrote:
>> > > On 11/20/2018 11:28 PM, Trent Piepho wrote:
>> > > > On Tue, 2018-11-20 at 21:42 +0100, Stefan Agner wrote:
>> > > > > On 20.11.2018 20:13, Trent Piepho wrote:
>> > > > > > It also seems to me that this doesn't need to be in the internal pci
>> > > > > > config access functions.  The driver shouldn't be reading registers
>> > > > > > that don't exist anyway.  It's really about trying to fix sysfs access
>> > > > > > to registers that don't exist.  So maybe it should be done there.
>> > > > >
>> > > > > That was my first approach, see:
>> > > >
>> > > > Yes, but that just used the pci device id which applies to every IMX
>> > > > design.
>> > > >
>> > > > It's also not totally correct, as it seems real registers after 0x200
>> > > > do work on imx6, and that would prevent access to them.
>> > >
>> > > I see that Lorenzo already accepted the patch in pci/dwc:
>> > >
>> > > https://git.kernel.org/pub/scm/linux/kernel/git/lpieralisi/pci.git/commit/?h=pci/dwc&id=f14eaec153aaebbe940ddd21e4198cc2abc927c2
>> > >
>> > > My tests show that this series breaks pci cards on 6qdl and I think it
>> > > should be reverted until a fix is found. Are you OK with this?
>> > >
>> > > Fixing might require an entirely different approach.
>> >
>> > I tried to reproduce this issue on Apalis iMX6 (i.MX 6Q) with a ath9k
>> > PCIe WiFi card, the issue you are seeing did not happen. My lspci looks
>> > as follows:
>> >
>> > root@...10c63d739:/# lspci -v
>> > 00:00.0 PCI bridge: Synopsys, Inc. Device abcd (rev 01) (prog-if 00
>> > [Normal decode])
>> >         Flags: bus master, fast devsel, latency 0, IRQ 255
>> >         Memory at 01000000 (32-bit, non-prefetchable) [size=1M]
>> >         Bus: primary=00, secondary=01, subordinate=ff, sec-latency=0
>> >         Memory behind bridge: 01100000-011fffff
>> >         [virtual] Expansion ROM at 01200000 [disabled] [size=64K]
>> >         Capabilities: [40] Power Management version 3
>> >         Capabilities: [50] MSI: Enable- Count=1/1 Maskable+ 64bit+
>> >         Capabilities: [70] Express Root Port (Slot-), MSI 00
>> >         Capabilities: [100] Advanced Error Reporting
>> >         Capabilities: [140] Virtual Channel
>> > lspci: Unable to load libkmod resources: error -12
>> >
>> > 01:00.0 Network controller: Qualcomm Atheros AR928X Wireless Network
>> > Adapter (PCI-Express) (rev 01)
>> >         Subsystem: Foxconn International, Inc. Device e007
>> >         Flags: bus master, fast devsel, latency 0, IRQ 312
>> >         Memory at 01100000 (64-bit, non-prefetchable) [size=64K]
>> >         Capabilities: [40] Power Management version 2
>> >         Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit-
>> >         Capabilities: [60] Express Legacy Endpoint, MSI 00
>> >         Capabilities: [90] MSI-X: Enable- Count=1 Masked-
>> >         Capabilities: [100] Advanced Error Reporting
>> >         Capabilities: [140] Virtual Channel
>> >         Capabilities: [160] Device Serial Number 00-00-00-00-00-00-00-00
>> >         Kernel driver in use: ath9k
>> >
>> >
>> > I did also setup a WiFi network and transmitted some packages, but I did
>> > not get a nobody carred message. Do you have an idea why that might be?
>> >
>> > # cat /proc/interrupts
>> > ...
>> > 312:      10967          0          0          0       GPC 123 Level    
>> > ath9k
>> > ...
>> >
>> >
>> > Your conclusion in this thread seem reasonable, hence reverting the
>> > issue does. However, I still would like to reproduce the issue so I can
>> > make sure that future patches don't break it :-)
>>
>> Hm, I realized that I need to enable CONFIG_PCIEPORTBUS and set
>> ath9k.use_msi=1 to get MSI for that card. However, it seems that ath9k
>> does not behave well in that setup. It does get interrupts, and seems to
>> work to some degree, but I was not successful in transmitting data over
>> WiFi, but that might be an entirly different thing.
>>
>> However, what I noticed is that when CONFIG_PCIEPORTBUS and
>> CONFIG_PCI_MSI is enabled, MSI works but legacy interrupt seem not to
>> fire anymore. That is true for ath9k as well as e1000e (using
>> e1000e.IntMode=0 to force legacy). Is that a known issue/limitation with
>> i.MX 6 PCIe?
> 
> Yes, this is a known issue with the Designware PCIe core, not just on
> i.MX6. As soon as any MSI interrupt is enabled, the core doesn't
> forward legacy IRQs anymore.

Oh I see, unfortunate!

> 
> So if any card in your system needs legacy interrupts (and ath9k is
> very likely to need this, as MSI support is pretty new and
> experimental), you need to boot with "nomsi" set on the kernel command
> line.

Ok, thanks for clarification.

FWIW, e1000e with MSI works perfectly fine, its just ath9k when forcing
MSI using the kernel parameter which does not work really. I guess that
is the reason it is not enabled by default.

--
Stefan

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