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Subject: Re: [PATCH net 1/4] net: freescale/fman: Split the main resource
 region reservation
To:     Madalin Bucur <madalin.bucur@nxp.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20201203135039.31474-1-patrick.havelange@essensium.com>
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From:   Patrick Havelange <patrick.havelange@essensium.com>
Message-ID: <8c28d03a-8831-650c-cf17-9a744d084479@essensium.com>
Date:   Wed, 9 Dec 2020 15:16:43 +0100
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>>> area. I'm assuming this is the problem you are trying to address here,
>>> besides the stack corruption issue.
>>
>> Yes exactly.
>> I did not add this behaviour (having a main region and subdrivers using
>> subregions), I'm just trying to correct what is already there.
>> For example: this is some content of /proc/iomem for one board I'm
>> working with, with the current existing code:
>> ffe400000-ffe4fdfff : fman
>>     ffe4e0000-ffe4e0fff : mac
>>     ffe4e2000-ffe4e2fff : mac
>>     ffe4e4000-ffe4e4fff : mac
>>     ffe4e6000-ffe4e6fff : mac
>>     ffe4e8000-ffe4e8fff : mac
>>
>> and now with my patches:
>> ffe400000-ffe4fdfff : /soc@ffe000000/fman@400000
>>     ffe400000-ffe480fff : fman
>>     ffe488000-ffe488fff : fman-port
>>     ffe489000-ffe489fff : fman-port
>>     ffe48a000-ffe48afff : fman-port
>>     ffe48b000-ffe48bfff : fman-port
>>     ffe48c000-ffe48cfff : fman-port
>>     ffe4a8000-ffe4a8fff : fman-port
>>     ffe4a9000-ffe4a9fff : fman-port
>>     ffe4aa000-ffe4aafff : fman-port
>>     ffe4ab000-ffe4abfff : fman-port
>>     ffe4ac000-ffe4acfff : fman-port
>>     ffe4c0000-ffe4dffff : fman
>>     ffe4e0000-ffe4e0fff : mac
>>     ffe4e2000-ffe4e2fff : mac
>>     ffe4e4000-ffe4e4fff : mac
>>     ffe4e6000-ffe4e6fff : mac
>>     ffe4e8000-ffe4e8fff : mac
>>
>>> While for the latter I think we can
>>> put together a quick fix, for the former I'd like to take a bit of time
>>> to select the best fix, if one is really needed. So, please, let's split
>>> the two problems and first address the incorrect stack memory use.
>>
>> I have no idea how you can fix it without a (more correct this time)
>> dummy region passed as parameter (and you don't want to use the first
>> patch). But then it will be useless to do the call anyway, as it won't
>> do any proper verification at all, so it could also be removed entirely,
>> which begs the question, why do it at all in the first place (the
>> devm_request_mem_region).
>>
>> I'm not an expert in that part of the code so feel free to correct me if
>> I missed something.
>>
>> BR,
>>
>> Patrick H.
> 
> Hi, Patrick,
> 
> the DPAA entities are described in the device tree. Adding some hardcoding in
> the driver is not really the solution for this problem. And I'm not sure we have

I'm not seeing any problem here, the offsets used by the fman driver 
were already there, I just reorganized them in 2 blocks.

> a clear problem statement to start with. Can you help me on that part?

- The current call to __devm_request_region in fman_port.c is not correct.

One way to fix this is to use devm_request_mem_region, however this 
requires that the main fman would not be reserving the whole region. 
This leads to the second problem:
- Make sure the main fman driver is not reserving the whole region.

Is that clearer like this ?

Patrick H.

> 
> Madalin
>