From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46654) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aLgzY-0005jf-MU for qemu-devel@nongnu.org; Tue, 19 Jan 2016 19:51:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aLgzX-00077V-KB for qemu-devel@nongnu.org; Tue, 19 Jan 2016 19:51:20 -0500 References: <5c18054d536f3f940d3059235f0ac4aad42c835c.1452359845.git.digetx@gmail.com> <20160112035858.GG3308@pcrost-box> <5695420E.2020709@gmail.com> From: Dmitry Osipenko Message-ID: <569ED9DB.6070508@gmail.com> Date: Wed, 20 Jan 2016 03:50:35 +0300 MIME-Version: 1.0 In-Reply-To: <5695420E.2020709@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v10 5/7] hw/ptimer: Legalize running with delta = load = 0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Crosthwaite Cc: Peter Maydell , qemu-arm@nongnu.org, QEMU Developers 12.01.2016 21:12, Dmitry Osipenko пишет: > 12.01.2016 06:58, Peter Crosthwaite пишет: >> On Sat, Jan 09, 2016 at 08:39:53PM +0300, Dmitry Osipenko wrote: >>> Currently ptimer would print error message and clear enable flag for an >>> arming timer that has delta = load = 0. That actually could be a valid case >>> for some hardware, like instant IRQ trigger for oneshot timer or continuous >>> in periodic mode. Support those cases by printing error message only when >>> period = 0. >>> >> >> Isn't the continuous-periodic the same as period = 0, so if we were to really >> support this, there should be no error message. This would simplify as we >> can remove the conditionals of 0 period completely and rely only on the >> too-fast clamps you add in previous patches. >> > > I don't think that clamping is needed. Instead doing the ptimer_tick might be > necessary, so ptimer user could handle that case on it own. > > BTW, that printf isn't quite reliable, hw_error or other way of execution abort > should been used instead. > > Thanks for the comment. > Just tried with the clamping. It works, but what clamping should be chosen for icount mode? delta * period = 1ns is damn slow. However, I'm still not sure what benefit has clamping over unclearable IRQ... only disadvantages in form of slowdown in icount mode, +2 lines of ptimer code and possible misbehaviour of blazing fast host machine in non-icount mode. -- Dmitry