[U-Boot] [PATCH 2/5] ls2080: Disable dcache during ddr init

[Alexander Graf]

On 13.05.16 18:28, York Sun wrote:
> On 05/13/2016 05:21 AM, Alexander Graf wrote:
>> While trying something completely different I saw the DDR probe hang on
>> boot reliably depending on how big my code ended up. Adding simple "nop"
>> instructions in my code (completely unrelated) flow made the DDR probe
>> work again.
>>
>> So we're accessing some RAM - probably the page table - and rely on the
>> cache to give us a correct view of the world while DRAM gets initialized.
>>
>> This patch just disables dcache while we're initializing the memory controller,
>> resolving all system hangs for me so far.
>>
>> Signed-off-by: Alexander Graf <agraf at suse.de>
>>
>> ---
>>
>> I guess the "real" solution would be to find out what exactly gets accessed in
>> such a case and then just map whatever it is into SRAM. Or maybe qixis_reset
>> doesn't fully reset something in the cache tolopogy and that wants to get
>> flushed out when we don't have ram yet? I don't know...
>> ---
>>  board/freescale/ls2080a/ddr.c    | 2 ++
>>  board/freescale/ls2080aqds/ddr.c | 2 ++
>>  board/freescale/ls2080ardb/ddr.c | 2 ++
>>  3 files changed, 6 insertions(+)
>>
>> diff --git a/board/freescale/ls2080a/ddr.c b/board/freescale/ls2080a/ddr.c
>> index 1827ddc..a02aa64 100644
>> --- a/board/freescale/ls2080a/ddr.c
>> +++ b/board/freescale/ls2080a/ddr.c
>> @@ -165,7 +165,9 @@ phys_size_t initdram(int board_type)
>>  	puts("Initializing DDR....");
>>  
>>  	puts("using SPD\n");
>> +	dcache_disable();
>>  	dram_size = fsl_ddr_sdram();
>> +	set_sctlr(get_sctlr() | (CR_C|CR_M));
> 
> Alex,
> 
> I can't agree with the proposed change. Having dcache has major speed boost
> during initializing, especially when we run it on an emulator. As you suggested
> in the note, the root cause needs to be identified. Qixis_reset has nothing to
> do with cache. It is a board-level FPGA control.

Yes, this patch is mostly FYI. I'm more than happy to not have it
applied - FWIW it's sheer luck that my compiler happened to emit the
instructions in the right place for things to work without any of the
other patches ;). So we might as well rely on luck with the others applied.


Alex