linux-kernel - Re: [PATCH 1/2] MIPS: Add barriers between dcache & icache flushes

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Date:   Mon, 06 Mar 2023 11:28:15 +0100
From:   Sven Eckelmann <sven@...fation.org>
To:     linux-mips@...ux-mips.org, Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...tec.com>
Cc:     Paul Burton <paul.burton@...tec.com>,
        James Hogan <james.hogan@...tec.com>,
        Joshua Kinard <kumba@...too.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        linux-kernel@...r.kernel.org,
        "Maciej W. Rozycki" <macro@...esourcery.com>,
        Markos Chandras <markos.chandras@...tec.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        David Bauer <mail@...id-bauer.net>
Subject: Re: [PATCH 1/2] MIPS: Add barriers between dcache & icache flushes

On Monday, 22 February 2016 19:09:44 CET Paul Burton wrote:
> Index-based cache operations may be arbitrarily reordered by out of
> order CPUs. Thus code which writes back the dcache & then invalidates
> the icache using indexed cache ops must include a barrier between
> operating on the 2 caches in order to prevent the scenario in which:
> 
>   - icache invalidation occurs.
> 
>   - icache fetch occurs, due to speculation.
> 
>   - dcache writeback occurs.
> 
> If the above were allowed to happen then the icache would contain stale
> data. Forcing the dcache writeback to complete before the icache
> invalidation avoids this.
> 
> Signed-off-by: Paul Burton <paul.burton@...tec.com>
> Cc: James Hogan <james.hogan@...tec.com>
> ---

What happened to this patch? Because it seems like it is required for some 
74kc devices to get them booting (instead of being stuck in an endless
tlbmiss_handler_setup_pgd loop):

* https://github.com/freifunk-gluon/gluon/issues/2784
* https://github.com/openwrt/openwrt/commit/ea6fb9c16dfb9763ea681803db65644b68bae873
* https://github.com/freifunk-gluon/gluon/pull/2810

Kind regards,
	Sven
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