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From:   Paul Burton <paul.burton@mips.com>
To:     Will Deacon <will.deacon@arm.com>
CC:     "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@linux.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrea Parri <andrea.parri@amarulasolutions.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        David Howells <dhowells@redhat.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Maciej W. Rozycki" <macro@linux-mips.org>,
        Ingo Molnar <mingo@kernel.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>, Tony Luck <tony.luck@intel.com>
Subject: Re: [PATCH 10/20] mips/mmiowb: Add unconditional mmiowb() to
 arch_spin_unlock()
Thread-Topic: [PATCH 10/20] mips/mmiowb: Add unconditional mmiowb() to
 arch_spin_unlock()
Thread-Index: AQHU0De1/M1S8jaEokePEKxrUNkxAKX3WFiA
Date:   Fri, 1 Mar 2019 22:16:18 +0000
Message-ID: <20190301221616.uhpjjepmxjmahkjt@pburton-laptop>
References: <20190301140348.25175-1-will.deacon@arm.com>
 <20190301140348.25175-11-will.deacon@arm.com>
In-Reply-To: <20190301140348.25175-11-will.deacon@arm.com>
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Hi Will,

On Fri, Mar 01, 2019 at 02:03:38PM +0000, Will Deacon wrote:
> The mmiowb() macro is horribly difficult to use and drivers will continue
> to work most of the time if they omit a call when it is required.
>=20
> Rather than rely on driver authors getting this right, push mmiowb() into
> arch_spin_unlock() for mips. If this is deemed to be a performance issue,
> a subsequent optimisation could make use of ARCH_HAS_MMIOWB to elide
> the barrier in cases where no I/O writes were performed inside the
> critical section.
>=20
> Signed-off-by: Will Deacon <will.deacon@arm.com>

Cleaning up our I/O functions has been on my to-do list for a while, so
I'll aim to get to that soon & get the calls to mmiowb_set_pending() in
place as part of it so that we can look at that optimization & drop the
custom queued_spin_unlock().

Meanwhile this looks sane & I don't want to hold it up so:

    Acked-by: Paul Burton <paul.burton@mips.com>

Thanks,
    Paul