Re: [PATCH v2 1/5] ArmPlatformPkg/FVP: map motherboard VRAM as uncached memory

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 6 April 2017 at 19:26, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> On Thu, Apr 06, 2017 at 02:15:47PM +0100, Ard Biesheuvel wrote:
>> The VRAM of the PL111 on the FVP Base/Foundation models is described as
>> device memory rather than uncached memory, which is not an accurate
>> description of the nature of the region (i.e., a framebuffer), and may
>> result in problems when using accelerated string routines to access the
>> region, since this may legally involve unaligned accesses or DC ZVA
>> instructions, which are not allowed on device mappings.
>>
>> So split of the 8 MB VRAM region into a separate region, and map it using
>> memory attributes.
>
> "Normal memory attributes"?
>

OK

>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  ArmPlatformPkg/ArmVExpressPkg/Include/Platform/RTSM/ArmPlatform.h  | 10 ++++++----
>>  ArmPlatformPkg/ArmVExpressPkg/Library/ArmVExpressLibRTSM/RTSMMem.c |  8 +++++++-
>>  2 files changed, 13 insertions(+), 5 deletions(-)
>>
>> diff --git a/ArmPlatformPkg/ArmVExpressPkg/Include/Platform/RTSM/ArmPlatform.h b/ArmPlatformPkg/ArmVExpressPkg/Include/Platform/RTSM/ArmPlatform.h
>> index 06414e6e7208..4e17c800a34f 100644
>> --- a/ArmPlatformPkg/ArmVExpressPkg/Include/Platform/RTSM/ArmPlatform.h
>> +++ b/ArmPlatformPkg/ArmVExpressPkg/Include/Platform/RTSM/ArmPlatform.h
>> @@ -40,9 +40,11 @@
>>  #define ARM_VE_SMB_SRAM_BASE                    0x2E000000
>>  #define ARM_VE_SMB_SRAM_SZ                      SIZE_64KB
>>  // USB, Ethernet, VRAM
>> -#define ARM_VE_SMB_PERIPH_BASE                  0x18000000
>> -#define PL111_CLCD_VRAM_MOTHERBOARD_BASE        ARM_VE_SMB_PERIPH_BASE
>> -#define ARM_VE_SMB_PERIPH_SZ                    SIZE_64MB
>> +#define ARM_VE_SMB_PERIPH_BASE                  0x18800000
>> +#define ARM_VE_SMB_PERIPH_SZ                    (SIZE_64MB - SIZE_8MB)
>> +
>> +#define PL111_CLCD_VRAM_MOTHERBOARD_BASE        0x18000000
>> +#define PL111_CLCD_VRAM_MOTHERBOARD_SIZE        SIZE_8MB
>>
>>  // DRAM
>>  #define ARM_VE_DRAM_BASE                        PcdGet64 (PcdSystemMemoryBase)
>> @@ -75,6 +77,6 @@
>>  #define PL111_CLCD_CORE_TILE_VIDEO_MODE_OSC_ID  1
>>
>>  // VRAM offset for the PL111 Colour LCD Controller on the motherboard
>> -#define VRAM_MOTHERBOARD_BASE                     (ARM_VE_SMB_PERIPH_BASE   + 0x00000)
>> +#define VRAM_MOTHERBOARD_BASE                     (PL111_CLCD_VRAM_MOTHERBOARD_BASE)
>>
>>  #endif
>> diff --git a/ArmPlatformPkg/ArmVExpressPkg/Library/ArmVExpressLibRTSM/RTSMMem.c b/ArmPlatformPkg/ArmVExpressPkg/Library/ArmVExpressLibRTSM/RTSMMem.c
>> index 14c7e8e1d672..70c17ae70478 100644
>> --- a/ArmPlatformPkg/ArmVExpressPkg/Library/ArmVExpressLibRTSM/RTSMMem.c
>> +++ b/ArmPlatformPkg/ArmVExpressPkg/Library/ArmVExpressLibRTSM/RTSMMem.c
>> @@ -21,7 +21,7 @@
>>  #include <ArmPlatform.h>
>>
>>  // Number of Virtual Memory Map Descriptors
>> -#define MAX_VIRTUAL_MEMORY_MAP_DESCRIPTORS          8
>> +#define MAX_VIRTUAL_MEMORY_MAP_DESCRIPTORS          9
>>
>>  // DDR attributes
>>  #define DDR_ATTRIBUTES_CACHED   ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK
>> @@ -130,6 +130,12 @@ ArmPlatformGetVirtualMemoryMap (
>>    VirtualMemoryTable[Index].Length = 2 * ARM_VE_SMB_PERIPH_SZ;
>>    VirtualMemoryTable[Index].Attributes = ARM_MEMORY_REGION_ATTRIBUTE_DEVICE;
>>
>> +  // VRAM
>> +  VirtualMemoryTable[++Index].PhysicalBase = PL111_CLCD_VRAM_MOTHERBOARD_BASE;
>> +  VirtualMemoryTable[Index].VirtualBase = PL111_CLCD_VRAM_MOTHERBOARD_BASE;
>> +  VirtualMemoryTable[Index].Length = PL111_CLCD_VRAM_MOTHERBOARD_SIZE;
>> +  VirtualMemoryTable[Index].Attributes = ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED;
>
> Hmm, looking at this made me a bit confused though. Normal uncached
> memory is certainly bufferable (that's basically what write-combining
> means).
>

It maps to MAIR attribute encoding 0x44, which translates as

Normal Memory, Outer Non-Cacheable, Inner Non-Cacheable

> This looks like a naming hangover from ARMv5 translation table format.
> Is it about time we clean this up?

The whole 'ARM_MEMORY_REGION_xxxx' intermediate namespace should be
removed, I think.

> Or have I sprained my brain?
>
> /
>     Leif
>
>> +
>>    // Map sparse memory region if present
>>    if (HasSparseMemory) {
>>      VirtualMemoryTable[++Index].PhysicalBase = SparseMemoryBase;
>> --
>> 2.9.3
>>