linux-kernel - Re: [PATCH] MIPS: disable MMID if GINVT is not usable

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Message-ID: <87h5zsgf45.fsf@BLaptop.bootlin.com>
Date: Fri, 04 Jul 2025 17:17:14 +0200
From: Gregory CLEMENT <gregory.clement@...tlin.com>
To: Thomas Bogendoerfer <tsbogend@...ha.franken.de>, Jiaxun Yang
 <jiaxun.yang@...goat.com>
Cc: Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, Théo Lebrun
 <theo.lebrun@...tlin.com>, Tawfik Bayouk <tawfik.bayouk@...ileye.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: disable MMID if GINVT is not usable

Thomas Bogendoerfer <tsbogend@...ha.franken.de> writes:

> On Wed, Jun 25, 2025 at 03:44:00PM +0100, Jiaxun Yang wrote:
>> 在2025年6月25日周三 下午2:27，Gregory CLEMENT写道：
>> 
>> Hi Gregory,
>> 
>> > If System-level Interconnect (aka Network on Chip) does not support
>> > the global invalidation, then MMID feature is not usable. Indeed the
>> > current implementation of MMID relies on the GINV* instruction.
>> 
>> Yes, it is the case if the NoC IP can't handle AMBA ACE DVM requests.
>> 
>> >
>> > Signed-off-by: Gregory CLEMENT <gregory.clement@...tlin.com>
>> > ---
>> >  arch/mips/Kconfig                    | 6 ++++++
>> >  arch/mips/include/asm/cpu-features.h | 5 ++++-
>> >  arch/mips/mobileye/Kconfig           | 2 ++
>> >  3 files changed, 12 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
>> > index 
>> > 1e48184ecf1ec8e29c0a25de6452ece5da835e30..05ce008459b89f03fa71d94429607feb9d06526f 
>> > 100644
>> > --- a/arch/mips/Kconfig
>> > +++ b/arch/mips/Kconfig
>> > @@ -2575,6 +2575,12 @@ config WAR_R10000_LLSC
>> >  config WAR_MIPS34K_MISSED_ITLB
>> >  	bool
>> > 
>> > +# Some I6500 based SoC do not support the global invalidation on their
>> > +# System-level Interconnect (aka Network on Chip), this have an
>> > +# influence on the MMID support.
>> > +config GINVT_UNSUPPORTED_NOC
>> > +	bool
>> > +
>> 
>> I believe this should be a DeviceTree property of CM node instead of Kconfig
>> hack.
>
> Either that or by a runtime check, if possible.

Unfortunately we can't detect at runtime this (lack of) feature on the
NoC, so it has to be a device tree property.

Gregory

>
> Thomas.
>
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]

-- 
Grégory CLEMENT, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com