From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxime Coquelin Subject: Re: [STLinux Kernel] [PATCH 3/4] clk: Provide always-on clock support Date: Sat, 28 Feb 2015 08:52:23 +0100 Message-ID: <54F173B7.9030305@st.com> References: <1425071674-16995-1-git-send-email-lee.jones@linaro.org> <1425071674-16995-4-git-send-email-lee.jones@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1425071674-16995-4-git-send-email-lee.jones-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lee Jones , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: mturquette-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, kernel-F5mvAk5X5gdBDgjK7y7TUQ@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org Hi Lee, On 02/27/2015 10:14 PM, Lee Jones wrote: > Lots of platforms contain clocks which if turned off would prove fatal. > The only way to recover from these catastrophic failures is to restart > the board(s). Now, when a clock is registered with the framework it is > compared against a list of provided always-on clock names which must be > kept ungated. If it matches, we enable the existing CLK_IGNORE_UNUSED > flag, which will prevent the common clk framework from attempting to > gate it during the clk_disable_unused() procedure. Please correct me if I'm wrong, but your patch does not fix the issue you had initially. Let's take an example: A clock is critical for the system, and should never be gated, so you add the CLK_IGNORE_UNUSED flag so that it is not disabled by clk_disable_unused() procedure. The same clock is also used by other IPs, for example spi 0 instance. When starting a spi transfer, clk_enable() is called on this clock, so its usecount becomes 1. Once transfer done, clk_disable() is called, usecount becomes 0 and the clock gets disabled: system freeze. BR, Maxime -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html