[U-Boot] [PATCH 4/9] tegra: Replace home grown mmu code with generic table approach

[Alexander Graf]

On 22.02.16 19:28, Stephen Warren wrote:
> On 02/21/2016 06:57 PM, Alexander Graf wrote:
>> Now that we have nice table driven page table creating code that gives
>> us everything we need, move to that.
> 
>> diff --git a/include/configs/tegra210-common.h
>> b/include/configs/tegra210-common.h
> 
>> +#define CONFIG_SYS_FULL_VA
>> +#define CONFIG_SYS_MEM_MAP {                        \
>> +    {                                \
>> +        .base = 0x0UL,                        \
>> +        .size = 0x80000000UL,                    \
>> +        .attrs = PTE_BLOCK_MEMTYPE(MT_DEVICE_NGNRNE) |        \
>> +             PTE_BLOCK_NON_SHARE |                \
>> +             PTE_BLOCK_PXN | PTE_BLOCK_UXN            \
>> +    }, {                                \
>> +        .base = 0x80000000UL,                    \
>> +        .size = 0xff80000000UL,                    \
>> +        .attrs = PTE_BLOCK_MEMTYPE(MT_NORMAL) |            \
>> +             PTE_BLOCK_INNER_SHARE                \
>> +    },                                \
>> +    }
> 
> I'd prefer a layout that didn't align the closing } for different
> nesting levels in the same column. To avoid indenting everything a lot,
> it seems simplest to pull the final } back into the first column.

Seems like people want this in as structs in board files rather than a
#define in a header anyway to enable more flexible code and ensure that
you can build the table based on dt. So there we have natural }
alignment again :).

> 
> I believe the .size field of the second entry in the array only needs to
> be 0x80000000. Testing with a PCIe Ethernet card on p2371-2180 (the
> driver for which sets up noncached entries in the page tables, hence
> should exercise all this code) confirms that.

I was surprised to see the full map in your code too, but I wanted to
make this patch with as little behavioral change as possible (for bisect
reasons). So the page table that gets constructed before and after
should be almost identical.

If we want to change behavior later on, I'd much rather like to see that
in a follow-up patch independent of this set.


Alex

> While recent Tegra systems do support more than 2GB of RAM, U-Boot will
> itself only use the first 2GB, so that PAs over 4GB are not used. See
> board_get_usable_ram_top() in arch/arm/mach-tegra/board2.c. That's
> because some peripherals can only access 32-bit PAs, and the simplest
> way to accommodate that is to ignore any RAM above the 32-bit limit.