linux-kernel - Re: [PATCH 3/5] MIPS: Move mips_cm_probe after prom

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Message-Id: <8d02a270-c9b7-4389-899e-cd755e55f0a4@app.fastmail.com>
Date: Wed, 08 May 2024 17:23:48 +0100
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Serge Semin" <fancer.lancer@...il.com>
Cc: "paulburton@...nel.org" <paulburton@...nel.org>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Rob Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 3/5] MIPS: Move mips_cm_probe after prom_init



在2024年5月8日五月 下午1:50，Serge Semin写道：
> On Tue, May 07, 2024 at 10:01:51AM +0100, Jiaxun Yang wrote:
>> Move mips_cm_probe after prom_init so we can use fdt functions
>> in mips_cm_probe to obtain essential information.
>> 
>> Impat for all systems that may have CM in system:
>
>> - geneirc: Adjusted code to accommodate this change
>
> s/geneirc/generic
>
>> - Lantiq: No impact, CM configuration won't be changed at all
>> - ralink: Called mips_cm_probe on it's own, in prom_init->prom_soc_init
>
>> - malta: No impact, CM address comes from CP0_CMGCR
>
> Are you sure about this? This was one of the problematic part I met
> back when was trying to implement the feature.
> arch/mips/mti-malta/malta-init.c:
> prom_init()
> +-> mips_cpc_probe()
>     +-> mips_cpc_phys_base()
>         +-> mips_cm_present(): mips_gcr_base != NULL
>         +-> read_gcr_cpc_status()
>         +-> read_gcr_cpc_base()
>         +-> write_gcr_cpc_base()
>
> So by moving mips_cm_probe() to being executed after prom_init() the
> calls-chain above will be broken since the mips_gcr_base will be left
> uninitialized. Do I miss something?

Hi Serge,

Good catch! This is indeed a problem.
I tried to dig a little bit and found that a possible solution is to
move SMP initialization to device_tree_init(), as what generic platform
did.

I was able to test malta boot with this solution on my heavily patched
QEMU, I can confirm that both CM-SMP and scache are working as expected.

Will share my QEMU patches and configurations in next rev. 

Thanks
- Jiaxun

>
> Please, note originally the mips_cm_probe() invocation was right
> above the Malta's mips_cpc_probe():
> 3af5a67c86a3 ("MIPS: Fix early CM probing")
>
> -Serge(y)
>
>> 
>> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>> ---
>>  arch/mips/kernel/setup.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
>> index 12a1a4ffb602..732579c8f4f8 100644
>> --- a/arch/mips/kernel/setup.c
>> +++ b/arch/mips/kernel/setup.c
>> @@ -773,8 +773,8 @@ static void __init setup_rng_seed(void)
>>  void __init setup_arch(char **cmdline_p)
>>  {
>>  	cpu_probe();
>> -	mips_cm_probe();
>>  	prom_init();
>> +	mips_cm_probe();
>>  
>>  	setup_early_fdc_console();
>>  #ifdef CONFIG_EARLY_PRINTK
>> 
>> -- 
>> 2.34.1
>> 
>>

-- 
- Jiaxun