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Date:   Wed, 6 Jan 2021 11:15:42 +0100
From:   Maxime Ripard <maxime@cerno.tech>
To:     Wilken Gottwalt <wilken.gottwalt@posteo.net>
Cc:     linux-kernel@vger.kernel.org, Ohad Ben-Cohen <ohad@wizery.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Baolin Wang <baolin.wang7@gmail.com>,
        Rob Herring <robh+dt@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@siol.net>
Subject: Re: [PATCH v5 2/2] hwspinlock: add sun6i hardware spinlock support
Message-ID: <20210106101542.zziwdyhq7arysrsj@gilmour>
References: <cover.1608721968.git.wilken.gottwalt@posteo.net>
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On Wed, Dec 23, 2020 at 12:35:10PM +0100, Wilken Gottwalt wrote:
> Adds the sun6i_hwspinlock driver for the hardware spinlock unit found in
> most of the sun6i compatible SoCs.
>=20
> This unit provides at least 32 spinlocks in hardware. The implementation
> supports 32, 64, 128 or 256 32bit registers. A lock can be taken by
> reading a register and released by writing a 0 to it. This driver
> supports all 4 spinlock setups, but for now only the first setup (32
> locks) seem to exist in available devices. This spinlock unit is shared
> between all ARM cores and the embedded companion core. All of them can
> take/release a lock with a single cycle operation. It can be used to
> sync access to devices shared by the ARM cores and the companion core.
>=20
> There are two ways to check if a lock is taken. The first way is to read
> a lock. If a 0 is returned, the lock was free and is taken now. If an 1
> is returned, the caller has to try again. Which means the lock is taken.
> The second way is to read a 32bit wide status register where every bit
> represents one of the 32 first locks. According to the datasheets this
> status register supports only the 32 first locks. This is the reason the
> first way (lock read/write) approach is used to be able to cover all 256
> locks in future devices. The driver also reports the amount of supported
> locks via debugfs.
>=20
> Signed-off-by: Wilken Gottwalt <wilken.gottwalt@posteo.net>

Reviewed-by: Maxime Ripard <mripard@kernel.org>

Thanks!
Maxime

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