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

From: Stefan Agner <stefan@agner.ch>
To: Leonard Crestez <leonard.crestez@nxp.com>
Cc: lorenzo.pieralisi@arm.com, Trent Piepho <tpiepho@impinj.com>,
	Richard Zhu <hongxing.zhu@nxp.com>,
	linux-kernel@vger.kernel.org, jingoohan1@gmail.com,
	gustavo.pimentel@synopsys.com, andrew.smirnov@gmail.com,
	linux-pci@vger.kernel.org, l.stach@pengutronix.de,
	bhelgaas@google.com
Subject: Re: [PATCH v3 2/2] PCI: imx6: limit DBI register length
Date: Wed, 28 Nov 2018 13:19:50 +0100	[thread overview]
Message-ID: <fd07b82d2473d5d7db9826142e79b00a@agner.ch> (raw)
In-Reply-To: <VI1PR04MB5533BBC2B45752ED84E4D037EEDA0@VI1PR04MB5533.eurprd04.prod.outlook.com>

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@ea210c63d739:/# 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 :-)

--
Stefan