From:   Sven Eckelmann <sven@narfation.org>
To:     linux-mips@linux-mips.org, Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@imgtec.com>
Cc:     Paul Burton <paul.burton@imgtec.com>,
        James Hogan <james.hogan@imgtec.com>,
        Joshua Kinard <kumba@gentoo.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        linux-kernel@vger.kernel.org,
        "Maciej W. Rozycki" <macro@codesourcery.com>,
        Markos Chandras <markos.chandras@imgtec.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        David Bauer <mail@david-bauer.net>
Subject: Re: [PATCH 1/2] MIPS: Add barriers between dcache & icache flushes
Date:   Mon, 06 Mar 2023 11:28:15 +0100
Message-ID: <4818332.31r3eYUQgx@ripper>
In-Reply-To: <1456164585-26910-1-git-send-email-paul.burton@imgtec.com>
References: <1456164585-26910-1-git-send-email-paul.burton@imgtec.com>
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From: Sven Eckelmann <sven@narfation.org>
Date: Mon, 06 Mar 2023 11:28:15 +0100
Message-ID: <4818332.31r3eYUQgx@ripper>
References: <1456164585-26910-1-git-send-email-paul.burton@imgtec.com>
MIME-Version: 1.0

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@imgtec.com>
> Cc: James Hogan <james.hogan@imgtec.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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