From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from imap.sh.mvista.com (unknown [63.81.120.155]) by ozlabs.org (Postfix) with ESMTP id 87500DDE1A for ; Fri, 18 May 2007 05:42:14 +1000 (EST) Message-ID: <464CB071.5050504@ru.mvista.com> Date: Thu, 17 May 2007 23:43:45 +0400 From: Sergei Shtylyov MIME-Version: 1.0 To: Segher Boessenkool Subject: Re: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver References: <200705172142.26739.sshtylyov@ru.mvista.com> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Cc: linuxppc-dev@ozlabs.org, mingo@elte.hu, tglx@linutronix.de, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Segher Boessenkool wrote: >> + * We must write a positive value to the decrementer to clear >> + * the interrupt on the IBM 970 CPU series. In periodic mode, >> + * this happens when the decrementer gets reloaded later, but >> + * in one-shot mode, we have to do it here since an event handler >> + * may skip loading the new value... > Nothing special about 970 here -- on *every* PowerPC, > a decrementer exception exists as long as the high > bit of the decrementer equals 1. BookE is different > of course. Some other CPUs might deviate from the > architecture as well. Quoting "PowerPC Operating Environment Architecture": The Decrementer counts down. On POWER4, a Decrementer exception occurs when DEC0 changes from 0 to 1. On POWER4+, operation is as follows. The exception effects of the Decrementer are said to be consistent with the contents of the Decrementer if one of the following statements is true. * DEC0=0 and a Decrementer exception does not exist. * DEC0=1 and a Decrementer exception exists. If DEC0=0, a context synchronizing instruction or event ensures that the exception effects of the Decrementer are consistent with the contents of the Decrementer. Otherwise, when the contents of DEC0 change, the exception effects of the Decrementer become consistent with the new contents of the Decrementer reasonably soon after the change. > Segher WBR, Sergei