From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933486AbbBQO0H (ORCPT ); Tue, 17 Feb 2015 09:26:07 -0500 Received: from arroyo.ext.ti.com ([192.94.94.40]:55925 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756785AbbBQO0F (ORCPT ); Tue, 17 Feb 2015 09:26:05 -0500 Message-ID: <54E34F73.2080108@ti.com> Date: Tue, 17 Feb 2015 16:25:55 +0200 From: Roger Quadros User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Robert Abel CC: , Tony Lindgren , , , Linux Kernel Maling List Subject: Re: [PATCH 2/4] ARM OMAP2+ GPMC: always program GPMCFCLKDIVIDER References: <1424101741-24152-1-git-send-email-rabel@cit-ec.uni-bielefeld.de> <1424101741-24152-2-git-send-email-rabel@cit-ec.uni-bielefeld.de> <1424101741-24152-3-git-send-email-rabel@cit-ec.uni-bielefeld.de> <54E2F803.3070901@ti.com> <54E34786.1010102@ti.com> In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/02/15 16:06, Robert Abel wrote: > Hi Roger, > > On Tue, Feb 17, 2015 at 2:52 PM, Roger Quadros wrote: >> nobody stops the DT binding from specifying a large enough "gpmc,wait-monitoring-ns" value. >> The driver must use that to scale the GPMC_CLK if it doesn't fit in the GPMC_FCLK. >> This feature can come separately though. So for now I was suggesting to set the divisor to 1. >> [...] >> AFAIK "gpmc,sync-clk-ps" is not specified for asynchronous devices so it defaults to 0 >> in the driver. > > As you have rightly pointed out, sync-clk-ps defaults to 0, i.e. > divider 1. My solution would work for people /now/ with different > gpmc,wait-monitoring-ns requirements. Of course, in general you're > right, the driver could compute that on its own. However, this > influences sampling behavior of the GPMC, which is somewhat strange > anyway. Since I lack a proper test setup and time to experiment with > the GPMC, I'd compromise on leaving sync-clk-ps default to 0, divider > defaults to 1. If somebody feels up to implementing driver-side > GPMC_CLK scaling, they might as well nix the dependency at that point > in time. Right now, keeping the dependency seems more useful to users > than killing it right away. one more thing to note is that just specifying sync-clk-ps in DT is not enough for asynchronous devices. The driver doesn't set gpmc_t->sync_clk if "gpmc,sync-read" or "gpmc,sync-write" was not set in the DT, which would be the case for asynchronous devices. > >> What I'm stressing on is that there shouldn't be any dependency on "gpmc,sync-clk-ps" for >> asynchronous devices. It also becomes easier to specify the wait-monitoring-ns as we don't need >> to cross reference with "sync-clk-ps". > > As an aside: There shouldn't be a dependency on the FCLK for > synchronous accesses either. The GPMC driver is in a somewhat terrible > state that synchronous protocols have to specify in ns, which get > scaled by the startup FCLK period... So this wrongful dependency > doesn't make my top ten, especially since it right now would fit a use > case. What is your proposal to make things better? And what is your use case that doesn't work with existing setup? cheers, -roger