Re: [PATCH net 1/4] net: freescale/fman: Split the main resource region reservation

From: Patrick Havelange
Date: Tue Dec 08 2020 - 09:56:39 EST


On 2020-12-03 16:47, Madalin Bucur wrote:
-----Original Message-----
From: Patrick Havelange <patrick.havelange@xxxxxxxxxxxxx>
Sent: 03 December 2020 15:51
To: Madalin Bucur <madalin.bucur@xxxxxxx>; David S. Miller
<davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Cc: Patrick Havelange <patrick.havelange@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>

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@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.