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

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Date: Wed, 8 May 2024 15:50:34 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: Paul Burton <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-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 3/5] MIPS: Move mips_cm_probe after prom_init

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?

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
> 
>