linux-kernel - Re: [PATCH RESEND] x86/devicetree: Add support for boot time interrupt mode config

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Date:   Tue, 11 Oct 2022 03:59:55 +0000
From:   Rahul Tanwar <rtanwar@...linear.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        linux-lgm-soc <linux-lgm-soc@...linear.com>
Subject: Re: [PATCH RESEND] x86/devicetree: Add support for boot time
 interrupt mode config

On 3/10/2022 5:08 pm, Rahul Tanwar wrote:
> Presently, init/boot time interrupt delivery mode is enumerated only
> for ACPI enabled systems by parsing MADT table or for older systems
> by parsing MP table. But for OF based x86 systems, it is assumed &
> fixed to legacy PIC mode.
> 
> Add support for configuration of init time interrupt delivery mode
> for x86 OF based systems by introducing a new boolean property
> 'intel,no-imcr' for interrupt-controller node of local APIC. This
> property emulates IMCRP Bit 7 of MP feature info byte 2 of MP
> floating pointer structure.
> 
> Defaults to legacy PIC mode if absent. Configures it to virtual wire
> compatibility mode if present.
> 


Any comments or concerns for this patch? IMHO, this configurability of 
pic_mode was missing for OF systems & it should benefit other x86 based 
OF platforms as well. Please let me know if i am missing anything about 
it or if you have other concerns.

Thanks,
Rahul


> Signed-off-by: Rahul Tanwar <rtanwar@...linear.com>
> ---
>   arch/x86/kernel/devicetree.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/devicetree.c b/arch/x86/kernel/devicetree.c
> index 5cd51f25f446..de14015317f8 100644
> --- a/arch/x86/kernel/devicetree.c
> +++ b/arch/x86/kernel/devicetree.c
> @@ -167,7 +167,15 @@ static void __init dtb_lapic_setup(void)
>   			return;
>   	}
>   	smp_found_config = 1;
> -	pic_mode = 1;
> +	if (of_property_read_bool(dn, "intel,no-imcr")) {
> +		pr_info("    Virtual Wire compatibility mode.\n");
> +		pic_mode = 0;
> +	}
> +	else {
> +		pr_info("    IMCR and PIC compatibility mode.\n");
> +		pic_mode = 1;
> +	}
> +
>   	register_lapic_address(lapic_addr);
>   }
>