From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40KNdl3F7TzDrSD for ; Mon, 9 Apr 2018 18:24:59 +1000 (AEST) Message-ID: <1523262286.11062.16.camel@kernel.crashing.org> Subject: Re: [PATCH 5/6] powerpc/powernv: implement opal_put_chars_nonatomic From: Benjamin Herrenschmidt To: Nicholas Piggin Cc: linuxppc-dev@lists.ozlabs.org Date: Mon, 09 Apr 2018 18:24:46 +1000 In-Reply-To: <20180409162314.20e486c3@roar.ozlabs.ibm.com> References: <20180409054056.27292-1-npiggin@gmail.com> <20180409054056.27292-6-npiggin@gmail.com> <1523253475.11062.10.camel@kernel.crashing.org> <20180409162314.20e486c3@roar.ozlabs.ibm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2018-04-09 at 16:23 +1000, Nicholas Piggin wrote: > On Mon, 09 Apr 2018 15:57:55 +1000 > Benjamin Herrenschmidt wrote: > > > On Mon, 2018-04-09 at 15:40 +1000, Nicholas Piggin wrote: > > > The RAW console does not need writes to be atomic, so implement a > > > _nonatomic variant which does not take a spinlock. This API is used > > > in xmon, so the less locking thta's used, the better chance there is > > > that a crash can be debugged. > > > > I find the term "nonatomic" confusing... > > I guess it is to go with the "atomic" comment for the hvsi console > case -- all characters must get to the console together or not at > all. Yeah ok, it's just that in Linux "atomic" usually means something else :-) Why not just call it "unlocked" which is what it's about and matches existing practices thorough the kernel ? > > don't we have a problem if we > > start hitting OPAL without a lock where we can't trust > > opal_console_write_buffer_space anymore ? I think we need to handle > > partial writes in that case. Maybe we should return how much was > > written and leave the caller to deal with it. > > Yes, the _nonatomic variant doesn't use opal_console_write_buffer_space > and it does handle partial writes by returning written bytes (although > callers generally tend to loop at the moment, we might do something > smarter with them later). > > > I was hoping (but that isn't the case) that by nonatomic you actually > > meant calls that could be done in a non-atomic context, where we can do > > msleep instead of mdelay. That would be handy for the console coming > > from the hvc thread (the tty one). > > Ah right, no. However we no longer loop until everything is written, so > the hvc console driver (or the console layer) should be able to deal with > that with sleeping. I don't think we need to put it at this level of the > driver, but I don't know much about the console code. Ok, so hopefully we shouldn't be hitting the delay.. Cheers, Ben.