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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Nicholas Piggin <npiggin@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Jiri Slaby <jslaby@suse.com>
Subject: Re: [PATCH 08/15] powerpc/powernv: implement opal_put_chars_atomic
In-Reply-To: <20180501203721.7b60fcd8@roar.ozlabs.ibm.com>
References: <20180430145558.4308-1-npiggin@gmail.com> <20180430145558.4308-9-npiggin@gmail.com> <1525168138.2325.100.camel@kernel.crashing.org> <20180501203721.7b60fcd8@roar.ozlabs.ibm.com>
Date:   Mon, 07 May 2018 20:35:42 +1000
Message-ID: <87zi1bbvnl.fsf@concordia.ellerman.id.au>
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Nicholas Piggin <npiggin@gmail.com> writes:

> On Tue, 01 May 2018 19:48:58 +1000
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
>
>> On Tue, 2018-05-01 at 00:55 +1000, Nicholas Piggin wrote:
>> > The RAW console does not need writes to be atomic, so relax
>> > opal_put_chars to be able to do partial writes, and implement an
>> > _atomic variant which does not take a spinlock. This API is used
>> > in xmon, so the less locking that is used, the better chance there
>> > is that a crash can be debugged.  
>> 
>> Same comment I already had :-) "atomic" in Linux tends to mean
>> something else (ie, atomic context), so I'd rather have something
>> like opal_put_chars_sync() or such...
>
> Oh yeah, I didn't ignore you, just... I thought atomic was okay.
> atomic *also* tends to mean happens atomically. I think the in
> atomic context meaning actually tends to be inatomic.
>
> Sync I actually thought could be more easily confused with
> synchronous vs asynchronous here.

I think we probably want opal_put_chars() to stay as it is.

And then add a variant for the call (just xmon?) that want lock free
behaviour.

opal_put_chars_unlocked() or something?

cheers