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Date:   Fri, 1 Mar 2019 22:16:18 +0000
From:   Paul Burton <>
To:     Will Deacon <>
CC:     "" <>,
        "" <>,
        "Paul E. McKenney" <>,
        Benjamin Herrenschmidt <>,
        Michael Ellerman <>,
        Arnd Bergmann <>,
        Peter Zijlstra <>,
        Andrea Parri <>,
        Palmer Dabbelt <>,
        Daniel Lustig <>,
        David Howells <>,
        Alan Stern <>,
        Linus Torvalds <>,
        "Maciej W. Rozycki" <>,
        Ingo Molnar <>,
        Yoshinori Sato <>,
        Rich Felker <>, Tony Luck <>
Subject: Re: [PATCH 10/20] mips/mmiowb: Add unconditional mmiowb() to

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.
> 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.
> Signed-off-by: Will Deacon <>

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 <>


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