linux-kernel - Re: [PATCH v3 2/2] PCI: imx6: limit DBI register length

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Date:   Wed, 28 Nov 2018 18:36:48 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Leonard Crestez <leonard.crestez@....com>, l.stach@...gutronix.de
Cc:     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 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?

--
Stefan