linux-kernel - Re: [PATCH v6 2/2] hwspinlock: add sun6i hardware spinlock support

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Message-ID: <20210301150608.014b807b@monster.powergraphx.local>
Date:   Mon, 1 Mar 2021 15:06:08 +0100
From:   Wilken Gottwalt <wilken.gottwalt@...teo.net>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Baolin Wang <baolin.wang7@...il.com>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>
Subject: Re: [PATCH v6 2/2] hwspinlock: add sun6i hardware spinlock support

On Mon, 1 Mar 2021 14:13:05 +0100
Maxime Ripard <mripard@...nel.org> wrote:

> On Sat, Feb 27, 2021 at 02:03:54PM +0100, Wilken Gottwalt wrote:
> > Adds the sun6i_hwspinlock driver for the hardware spinlock unit found in
> > most of the sun6i compatible SoCs.
> >
> > 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.
> >
> > 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.
> >
> > Signed-off-by: Wilken Gottwalt <wilken.gottwalt@...teo.net>

Nope, I had to replace the devm_hwspin_lock_register function by the
hwspin_lock_register function because like Bjorn pointed out that it can
fail and needs to handled correctly. And having a devm_* function does not
play well with the non-devm clock/reset functions and winding back if an
error occurs. It also messes with the call order in the remove function. So
I went back to the classic way where I have full control over the call order.

> Didn't I review this one already?
> Maxime