[PATCH 05/14] at91: use structure to store the current soc

[ryan@bluewatersys.com (Ryan Mallon)]

On 04/29/2011 11:06 AM, Jean-Christophe PLAGNIOL-VILLARD wrote:
> On 08:20 Fri 29 Apr     , Ryan Mallon wrote:
>> On 04/29/2011 02:10 AM, Jean-Christophe PLAGNIOL-VILLARD wrote:
>>> On 16:04 Thu 28 Apr     , Andrew Victor wrote:
>>>> hi,
>>>>
>>>>>> If this eventually reduces code size then I think it is useful, but
>>>>>> otherwise I'm not sure I see the point?
>>>>> It's on purpose as the dbgu physical address is not at the same place
>>>>> so read the other register really does not impact the chip but if we do it
>>>>> later duting the boot or the life to the kernel it's an other story
>>>>>
>>>>> so the split between __cpu_is and cpu_is is necessarly
>>>>>
>>>>> all of this work is in preparation to allow multiple soc in the same kernel
>>>>> that's also why I map the system controller the same way on all at91 arm9
>>>>
>>>> The cpu_is() or__cpu_is() perform a at91_sys_read() of one of the DBGU
>>>> registers.
>>>>
>>>> But the address of the DBGU differs between CPUs regardless if you map
>>>> the system controller the same:
>>>>    at572d940hf.h:#define AT91_DBGU	(0xfffff200 - AT91_BASE_SYS)
>>>>    at91cap9.h:#define AT91_DBGU	(0xffffee00 - AT91_BASE_SYS)
>>>>    at91rm9200.h:#define AT91_DBGU	(0xfffff200 - AT91_BASE_SYS)
>>>>    at91sam9260.h:#define AT91_DBGU	(0xfffff200 - AT91_BASE_SYS)
>>>>    at91sam9261.h:#define AT91_DBGU	(0xfffff200 - AT91_BASE_SYS)
>>>>    at91sam9263.h:#define AT91_DBGU	(0xffffee00 - AT91_BASE_SYS)
>>>>    at91sam9g45.h:#define AT91_DBGU	(0xffffee00 - AT91_BASE_SYS)
>>>>    at91sam9rl.h:#define AT91_DBGU	(0xfffff200 - AT91_BASE_SYS)
>>>>
>>>> So I don't see how you can "detect" the CPU without first knowing
>>>> which CPU and therefore where the DBGU register is anyway.
>>>> And probing different addresses for a value is not an acceptable solution.
>>>>
>>>>
>>>> While having a single kernel image that supports AT91 processors is a
>>>> good goal, the soc.h is a totally unnecessary complication.
>>>> I can't think of any situation where an AT91 board.c file doesn't know
>>>> what processor it has.
>>>>
>>>> So instead of :
>>>>    boardXYZ-init ->  at91_initialize() --> magic-cpu-detection -->
>>>> at91XX_initialize()
>>>> just do:
>>>>    boardXYZ-init  -> at91XX_initialize()
>>> except there is no need to known it and board seach as the usb-926x are the
>>> same nearly and do not need to known on which soc they are
>>>
>>> ditto for other boards you do not need to known the soc we are on.
>>> And when you work on CPU module the board is the same but not the cpu on the
>>> module so detect the SOC allow to have one kernel for all and not multiple
>>> machine ID for each module and board combination
>>
>> I Agree with Andrew. When can determine everything we need from the
>> mach-type. For boards such as the usb-926x we have two separate
>> mach-types for the 9263 and the 9260 variants. The init_machine callback
>> can be separated in this case so that both of the boards initialise the
>> correct cpu type.
> I do work on board where is the case and I do not want to keep the limitation
> and yes I'll put them mainline
> 
> And Russell will not accept I'll create 10 or 20 machine ID for board / cpu
> module combinaison just because of different I do not detect the SOC type
> 
> so I'll continue to detect the soc

How? It has been pointed out that there is no way that this can be
reliably done if you have all of the at91 socs built into a single
kernel. You cannot know where the DBGU registers are to read determine
the cpu/soc type.

The most reliable way to do this, which also requires the least code, is
to have the boards explicitly specify which cpu/soc type they are. In
this case most of the cpu detection code can be removed. Only the minor
variant (i.e. 9260/9G20) detection code would need to remain.

~Ryan

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