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

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Date:   Thu, 10 Dec 2020 09:49:25 +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 2020-12-09 19:55, Madalin Bucur wrote:
>> -----Original Message-----
>> From: Patrick Havelange <patrick.havelange@...ensium.com>
>> Sent: 09 December 2020 16:17
>> 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
>> Subject: Re: [PATCH net 1/4] net: freescale/fman: Split the main resource
>> region reservation
>>
>>>>> 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.
>>>
>>> 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.

Hi,

> 
> The overlapping IO areas result from the device tree description, that in turn
> mimics the HW description in the manual. If we really want to remove the nesting,
> we should change the device trees, not the drivers.

But then that change would not be compatible with the existing device 
trees in already existing hardware. I'm not sure how to handle that case 
properly.

> If we want to hack it,
> instead of splitting ioremaps, we can reserve 4 kB in the FMan driver,
> and keep the ioremap as it is now, with the benefit of less code churn.

but then the ioremap and the memory reservation do not match. Why bother 
at all then with the mem reservation, just ioremap only and be done with 
it. What I'm saying is, I don't see the point of having a "fake" 
reservation call if it does not correspond that what is being used.

> In the end, what the reservation is trying to achieve is to make sure there
> is a single driver controlling a certain peripeheral, and this basic
> requirement would be addressed by that change plus devm_of_iomap() for child
> devices (ports, MACs).

Again, correct me if I'm wrong, but with the fake mem reservation, it 
would *not* make sure that a single driver is controlling a certain 
peripheral.

My point is, either have a *correct* mem reservation, or don't have one 
at all. There is no point in trying to cheat the system.

Patrick H.

> 
> Madalin
>