[PATCH 0/9] Switch internal registers address to 0xF1 on Armada 370/XP

[Gregory CLEMENT]

On 05/22/2013 04:33 PM, Arnd Bergmann wrote:
> On Tuesday 21 May 2013, Thomas Petazzoni wrote:
>> Unfortunately, for Armada 370 and Armada XP, the current generation of
>> bootloaders that are being shipped on Marvell evaluation boards, but
>> also on products like the Plathome OpenBlocks AX3 or the Globalscale
>> Mirabox do not do the remapping, and are leaving the internal
>> registers at 0xD0000000.
>>
>> However, this is causing some problems:
>>
>>  1 The internal registers window sits at 3 GB, in the middle of the
>>    0-4 GB area of physical memory, which is quite annoying when you
>>    have more than 3 GB of memory. Having them at 0xF1000000 means that
>>    you lose less RAM when you have more than 3 GB of physical memory
>>    installed. And since Armada XP is LPAE capable, you can even have
>>    more than 4 GB memory: we already have boards with 8 GB of memory
>>    installed.
> 
> Just for completeness:
> 
> Do any of the machines that use the old boot loader have more
> than 3 GB of memory?

As far as I know at least the Armada XP GP boards.

Moreover the OpenBlocks AX3 have non soldered memory, so
it could be possible to plug any amount of memory you want.
Howevere it is true that in this case you will have to update the
bootloader to setup the memory chip.

> 
>>  2 This is different from Kirkwood and Dove, which makes sharing some
>>    early code like earlyprintk complicated, while our goal is
>>    ultimately to merge all Marvell EBU platforms into mach-mvebu.
>>
>> (1) is really the primary motivation here, (2) is only a nice
>> side-effect.
>>
>> So, the new generation of bootloaders that are shipped on new Marvell
>> Armada 370/XP platforms are doing the remapping at 0xF1000000 prior to
>> starting Linux. The current kernel cannot boot on such platforms.
> 
> Does it boot if you disable the DEBUG_LL code and apply your
> patches 1-8? The reason I'm asking is that you already cannot have
> DEBUG_LL on a multiplatform kernel targeted at systems which don't
> use the same UART. Adding a further restriction that they must map
> the internal registers to the same physical address does not change
> this a lot.

Thomas will confirm, but I am pretty sure he also made test without
DEBUG_LL

> 
>> Therefore, the last patch of this series adds some early code in the
>> kernel, at the ->map_io() stage, to switch the internal registers from
>> 0xD0000000 to 0xF1000000 if this has not been done already by the
>> bootloader. As it was explained above, we unfortunately can't read the
>> current base address of the internal register window, so we need a
>> different mechanism to know if the bootloader has done the remapping
>> at 0xF1000000 (new generation bootloader) or has left the internal
>> registers at 0xD0000000 (old generation bootloader). In order to
>> distinguish between those two cases, a CP15 bit is being used. Old
>> bootloaders do not touch this CP15, so it is set to 0. New bootloaders
>> set this CP15 bit to 1, so that the kernel knows that the remapping
>> has already been done. The ->map_io() code looks at this bit to know
>> if the remapping should be done or not.
> 
> As you already admit, using the CP15 register is a hack. It sounds
> to me that a cleaner approach would be to put the correct address
> into the device tree and use that value everywhere, rather than
> hardcoding one or more addresses.

That means reading and decoding the device tree very early in the
auto-uncompress part of the kernel.

> 
>> Unfortunately, tweaking ->map_io() is not sufficient: we also want
>> earlyprintk to work. And earlyprintk is used *before* ->map_io() is
>> called, and *after* ->map_io() is called.
> 
> Note that by the time map_io is called, we no longer care about
> the physical address, since the uart is only accessed through the
> virtual mapping after __enable_mmu.
> 
> 	Arnd
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com