[RFC PATCH 1/1] arm: mach-k3: Enable icache on am625 to boot faster

[Andrew Davis]

On 11/9/23 11:37 AM, Nishanth Menon wrote:
> On 11:09-20231109, Joao Paulo Goncalves wrote:
>> Enable the am625 instruction cache on SPL and U-boot earlier for the A53
>> to execute code a bit faster. For normal boot flow, it was possible to
>> gain about 2 seconds on boot time.
>>
>> Signed-off-by: Joao Paulo Goncalves <joao.goncalves at toradex.com>
>> ---
>> Hello all,
>>
>> We are trying to optimize boot time on our AM62 devices and on TI community
>> forum [1] someone advised to enable ICACHE for am625. We enabled it, tested and got
>> around 2 seconds faster boot on storage media and about 5 seconds with DFU
>> for downloading images from A53 SPL. However, we don't know if this is the correct
>> solution and want more comments on this or why the ICACHE was not enabled by TI in
>> the first place.
>>
>> [1] https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1217839/am625-boot-time-between-a53-spl-and-a53-u-boot
>>
>> Regards,
>> Joao Paulo Goncalves
>>
>>   arch/arm/mach-k3/am625_init.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/mach-k3/am625_init.c b/arch/arm/mach-k3/am625_init.c
>> index 8fa36f7b91..d665d07b0b 100644
>> --- a/arch/arm/mach-k3/am625_init.c
>> +++ b/arch/arm/mach-k3/am625_init.c
>> @@ -210,6 +210,9 @@ void board_init_f(ulong dummy)
>>   			panic("DRAM init failed: %d\n", ret);
>>   	}
>>   	spl_enable_dcache();
>> +
>> +	if (!IS_ENABLED(CONFIG_CPU_V7R) && !IS_ENABLED(CONFIG_SYS_ICACHE_OFF))
>> +		icache_enable();
>>   }
>>   
>>   u32 spl_mmc_boot_mode(struct mmc *mmc, const u32 boot_device)
>> -- 
>> 2.34.1
> 
> Just noticed that icache_enable was missed for all of k3 as well - I
> suspect this is a miss rather than anything consciously done. btw
> icache_enable is already wrapped correctly under CONFIG_SYS_ICACHE_OFF in
> cache_v8.c
> 

For U-Boot proper, both I/D caches are enabled early in board_init_r().
Oddly the SPL version of this function does not do that. Some boards seem
to work around this by adding it manually, others must have missed this.
Maybe due to armv7/start.S doing this for us already, but not armv8/start.S..

We enable Icache in SPL for our CPU_V7R case inside setup_mpu_regions()(??)
We also enable Dcache in spl_enable_dcache(), maybe this should be
renamed spl_enable_cache() and it call enable_caches() which enables
both. Just be careful to invalidate the icache when enabling after
relocation.

This would be temporary, better solution would be to add it to the
SPL common board_init_r() to match the U-Boot one, that way all these
platforms wouldn't need to do it in their current inconsistent ways.

Andrew