[U-Boot] [PATCH 13/18] arm: K3: am654: Map common EEPROM data into SRAM scratch space

[Andrew F. Davis]

On 5/8/19 11:52 PM, Lokesh Vutla wrote:
> 
> 
> On 09/05/19 3:07 AM, Andreas Dannenberg wrote:
>> The board detection scheme employed on various TI EVMs makes use of
>> SRAM scratch space to share data read from an on-board EEPROM between
>> the different bootloading stages. Map the associated definition that's
>> used to locate this data into the SRAM scratch space we use on AM654x.
>>
>> Signed-off-by: Andreas Dannenberg <dannenberg at ti.com>
>> ---
>>  arch/arm/mach-k3/include/mach/am6_hardware.h | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/mach-k3/include/mach/am6_hardware.h b/arch/arm/mach-k3/include/mach/am6_hardware.h
>> index 3343233aa3..6df7631545 100644
>> --- a/arch/arm/mach-k3/include/mach/am6_hardware.h
>> +++ b/arch/arm/mach-k3/include/mach/am6_hardware.h
>> @@ -44,4 +44,7 @@
>>  #define CTRLMMR_LOCK_KICK1				0x0100c
>>  #define CTRLMMR_LOCK_KICK1_UNLOCK_VAL			0xd172bc5a
>>  
>> +/* MCU SCRATCHPAD usage */
>> +#define TI_SRAM_SCRATCH_BOARD_EEPROM_START CONFIG_SYS_K3_MCU_SCRATCHPAD_BASE
> 
> Won't HS devices fail while accessing this region? We should drop it altogether.
> 

HS devices cannot read this before SYSFW is loaded as by default it is
left firewalled by ROM. This read happens after SYSFW loading so it does
work currently, but no guarantee SYSFW will always remove this firewall
by default, we may need a driver that does an explicit device get for
this region to be sure it is powered and accessible (it is on a
different reset domain, it may need special handling).

I think we should avoid using this scratchpad for a couple other
reasons. After R5 SPL has finished bootloading is handled by A53 cores,
the R5 will be repurposed and other software will run on it, possibly
wiping out the memory here. Anything we want to pass form R5 to A53
should use a non-R5-local memory, not this scratchpad. We need the same
for passing the original boot media info also.

A lot of pitfalls for just 512 bytes of RAM..

Andrew

> Thanks and regards,
> Lokesh
> 
>> +
>>  #endif /* __ASM_ARCH_AM6_HARDWARE_H */
>>
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