From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aaro Koskinen <aaro.koskinen@nokia.com>
Subject: Re: [PATCH] OMAP2: gptimer min_delta_ns should be rounded up
Date: Tue, 30 Dec 2008 18:50:45 +0200
Message-ID: <495A5165.1040105@nokia.com>
References: <> <1230570868-25078-1-git-send-email-Aaro.Koskinen@nokia.com> <13B9B4C6EF24D648824FF11BE8967162036D3BCB12@dlee02.ent.ti.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Return-path: <linux-omap-owner@vger.kernel.org>
Received: from smtp.nokia.com ([192.100.122.230]:51915 "EHLO
	mgw-mx03.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751551AbYL3Quy (ORCPT
	<rfc822;linux-omap@vger.kernel.org>); Tue, 30 Dec 2008 11:50:54 -0500
In-Reply-To: <13B9B4C6EF24D648824FF11BE8967162036D3BCB12@dlee02.ent.ti.com>
Sender: linux-omap-owner@vger.kernel.org
List-Id: linux-omap@vger.kernel.org
To: "ext Woodruff, Richard" <r-woodruff2@ti.com>
Cc: "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>

Hello,

Woodruff, Richard wrote:
>> +             clockevent_delta2ns(1, &clockevent_gpt) + 1;
> 
> That value is still not correct.

[...]

>         clockevent_delta2ns(3, &clockevent_gpt);
> 
> min_delta_ns stops the frame work from trying to program an expiry time which may not be achievable due to timer costs.
> 
> A write to the timer when it has a 32KHz F-Clock can take ~3 32Khz clock cycles to complete.  Hence the cost of '3' not '1'.

I'm not sure if I see any problem. If the timer programming cost is 
bigger than min_delta_ns, the framework should adapt to it.

I guess you would want to make min_delta_ns bigger to avoid excessive 
scheduling/wakeups, but I think there is no any single "correct" value 
for every system/board.

A.