linux-kernel - Re: [PATCH 0/5] Modularize PCI

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Message-ID: <56CEB7BC.7010803@ti.com>
Date:	Thu, 25 Feb 2016 13:43:48 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	<linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	<devicetree@...r.kernel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grant Likely <grant.likely@...aro.org>,
	Ley Foon Tan <lftan@...era.com>,
	Murali Karicheri <m-karicheri2@...com>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Stanimir Varbanov <svarbanov@...sol.com>,
	Thierry Reding <thierry.reding@...il.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-arm-msm@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 0/5] Modularize PCI_DW related drivers.

Hi Arnd,

On Wednesday 24 February 2016 02:34 PM, Arnd Bergmann wrote:
> On Wednesday 24 February 2016 11:39:26 Kishon Vijay Abraham I wrote:
>> Hi,
>>
>> On Monday 08 February 2016 05:30 AM, Paul Gortmaker wrote:
>>> In a recent patch series that aimed to remove code related to module
>>> unload for PCI support that was simply non modular, the discussion
>>> led to people wanting to keep the code and push towards taking the
>>> steps needed to support moving it towards tristate instead[1].
>>>
>>> Here, we take step one, which is simply making the Kconfig change
>>> and then dealing with any build fallout or modpost fallout.  What
>>> amounts to essentially a sanity build test.  To be clear, these
>>> have not been runtime validated; that will need to be done by those
>>> with access to real hardware.  However, the changes are not anything
>>> that should disrupt any existing built-in validation, so real world
>>> users should not be impacted by this change.
>>>
>>> We start with a smaller family of drivers; those that actively select
>>> PCI_DW, as a nice self contained group to test the waters and see if
>>> everyone is still good with this approach before investing more time
>>> on a wider scale to other pci/host/ code blocks.
>>>
>>> As such the drivers here share a dependency on having the same group
>>> of functions exported in order to successfully complete modpost.
>>>
>>> In addition, we have to stray outside drivers/pci to add exports
>>> in two places; once for an ARM fault handler, and once for an OF
>>> variable.
>>>
>>> The pci-keystone-dw.c instance was handled separately because it
>>> consists of two source files that need their own group of driver
>>> specific exports above and beyond the "shared" ones.
>>>
>>> Then we convert the Kconfig for all remaining at once; we could have
>>> done it on a per driver basis for ease of revert if anyone really
>>> objects, but since it would be a one line change, that seemed like
>>> not a real concern.
>>>
>>> Build testing was done on the linux-next tree for arm allmodconfig.
>>
>> I took these patches and gave a test with DRA7xx board. As expected there was
>> no issues when the driver was built-in. However when I tried to rmmod/modprobe
>> I got this error [2].
> 
> Thanks for testing this!
> 
>> [2] -> http://pastebin.ubuntu.com/15185894/
> 
> It looks like you are hitting the BUG_ON() in ioremap_pte_range()
> that checks if a virtual address already has a page table entry,
> which in turn is probably a result of dw_pcie_host_init()
> calling pci_remap_iospace() again for the same memory area
> it has called the last time, and no cleanup done inbetween.
> 
> Could you try adding a pci_unmap_iospace() and calling that
> in the device remove function? Let me know if you need help
> implementing it.

That didn't look straight forward to me :-( I'll try to see this next week. Any
help from you will make it simpler for me.

Thanks
Kishon