From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751848AbbEGHhP (ORCPT ); Thu, 7 May 2015 03:37:15 -0400 Received: from down.free-electrons.com ([37.187.137.238]:47241 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750924AbbEGHhJ (ORCPT ); Thu, 7 May 2015 03:37:09 -0400 Date: Thu, 7 May 2015 09:37:02 +0200 From: Boris Brezillon To: Stephen Boyd Cc: Mike Turquette , linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Jonathan Corbet , Shawn Guo , ascha Hauer , David Brown , Daniel Walker , Bryan Huntsman , Tony Lindgren , Paul Walmsley , Liviu Dudau , Sudeep Holla , Lorenzo Pieralisi , Ralf Baechle , Max Filippov , Heiko Stuebner , Sylwester Nawrocki , Tomasz Figa , Barry Song , Viresh Kumar , Emilio =?UTF-8?B?TMOzcGV6?= , Maxime Ripard , Peter De Schrijver , Prashant Gaikwad , Stephen Warren , Thierry Reding , Alexandre Courbot , Tero Kristo , Ulf Hansson , Michal Simek , Philipp Zabel , linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-omap@vger.kernel.org, linux-mips@linux-mips.org, patches@opensource.wolfsonmicro.com, linux-rockchip@lists.infradead.org, linux-samsung-soc@vger.kernel.org, spear-devel@list.st.com, linux-tegra@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, rtc-linux@googlegroups.com Subject: Re: [PATCH v2 1/2] clk: change clk_ops' ->round_rate() prototype Message-ID: <20150507093702.0b58753d@bbrezillon> In-Reply-To: <20150507063953.GC32399@codeaurora.org> References: <1430407809-31147-1-git-send-email-boris.brezillon@free-electrons.com> <1430407809-31147-2-git-send-email-boris.brezillon@free-electrons.com> <20150507063953.GC32399@codeaurora.org> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Stephen, On Wed, 6 May 2015 23:39:53 -0700 Stephen Boyd wrote: > On 04/30, Boris Brezillon wrote: > > Clock rates are stored in an unsigned long field, but ->round_rate() > > (which returns a rounded rate from a requested one) returns a long > > value (errors are reported using negative error codes), which can lead > > to long overflow if the clock rate exceed 2Ghz. > > > > Change ->round_rate() prototype to return 0 or an error code, and pass the > > requested rate as a pointer so that it can be adjusted depending on > > hardware capabilities. > > > > Signed-off-by: Boris Brezillon > > Tested-by: Heiko Stuebner > > Tested-by: Mikko Perttunen > > Reviewed-by: Heiko Stuebner > > This patch is fairly invasive, and it probably doesn't even > matter for most of these clock providers to be able to round a > rate above 2GHz. Fair enough. > I've been trying to remove the .round_rate op > from the framework by encouraging new features via the > .determine_rate op. Oh, I wasn't aware of that (BTW, that's a good thing). Maybe this should be clearly stated (both in the struct clk_ops kerneldoc header and in Documentation/clk.txt). > Sadly, we still have to do a flag day and > change all the .determine_rate ops when we want to add things. Yes, but the number of clk drivers implementing ->determine_rate() is still quite limited compared to those implementing ->round_rate(). > > What if we changed determine_rate ops to take a struct > clk_determine_info (or some better named structure) instead of > the current list of arguments that it currently takes? Then when > we want to make these sorts of framework wide changes we can just > throw a new member into that structure and be done. I really like this idea, especially since I was wondering if we could pass other 'clk rate requirements' like the rounding policy (down, closest, up), or the maximum clk inaccuracy. > > It doesn't solve the unsigned long to int return value problem > though. We can solve that by gradually introducing a new op and > handling another case in the rounding path. If we can come up > with some good name for that new op like .decide_rate or > something then it makes things nicer in the long run. I like the > name .determine_rate though :/ Why not changing the ->determine_rate() prototype. As said above, the number of clk drivers implementing this function is still quite limited, and I guess we can have an ack for all of them. > > The benefit of all this is that we don't have to worry about > finding the random clk providers that get added into other > subsystems and fixing them up. If drivers actually care about > this problem then they'll be fixed to use the proper op. FYI, > last time we updated the function signature of .determine_rate we > broke a couple drivers along the way. > Hm, IMHO, adding a new op is not a good thing. I agree that it eases the transition, but ITOH you'll have to live with old/deprecated ops in your clk_ops structure with people introducing new drivers still using the old ops (see the number of clk drivers implementing ->round_rate() instead of ->determine_rate()). Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com