Date:   Tue, 8 Dec 2020 15:55:54 +0100
From:   Patrick Havelange <patrick.havelange@...ensium.com>
To:     Madalin Bucur <madalin.bucur@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net 1/4] net: freescale/fman: Split the main resource
 region reservation

On 2020-12-03 16:47, Madalin Bucur wrote:
>> -----Original Message-----
>> From: Patrick Havelange <patrick.havelange@...ensium.com>
>> Sent: 03 December 2020 15:51
>> To: Madalin Bucur <madalin.bucur@....com>; David S. Miller
>> <davem@...emloft.net>; Jakub Kicinski <kuba@...nel.org>;
>> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
>> Cc: Patrick Havelange <patrick.havelange@...ensium.com>
>> Subject: [PATCH net 1/4] net: freescale/fman: Split the main resource
>> region reservation
>>
>> The main fman driver is only using some parts of the fman memory
>> region.
>> Split the reservation of the main region in 2, so that the other
>> regions that will be used by fman-port and fman-mac drivers can
>> be reserved properly and not be in conflict with the main fman
>> reservation.
>>
>> Signed-off-by: Patrick Havelange <patrick.havelange@...ensium.com>
> 
> I think the problem you are trying to work on here is that the device
> tree entry that describes the FMan IP allots to the parent FMan device the
> whole memory-mapped registers area, as described in the device datasheet.
> The smaller FMan building blocks (ports, MDIO controllers, etc.) are
> each using a nested subset of this memory-mapped registers area.
> While this hierarchical depiction of the hardware has not posed a problem
> to date, it is possible to cause issues if both the FMan driver and any
> of the sub-blocks drivers are trying to exclusively reserve the registers
> 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@...000000/fman@...000
   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.

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