From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Heiko =?ISO-8859-1?Q?St=FCbner?= To: Jerome Brunet Cc: Michael Turquette , Stephen Boyd , linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Stephen Boyd , Shawn Guo , Dong Aisheng Subject: Re: [PATCH v2 4/8] clk: migrate the count of orphaned clocks at init Date: Thu, 15 Feb 2018 22:01:52 +0100 Message-ID: <1970074.VYjjbDuVRv@diego> In-Reply-To: <20180214134340.17242-5-jbrunet@baylibre.com> References: <20180214134340.17242-1-jbrunet@baylibre.com> <20180214134340.17242-5-jbrunet@baylibre.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" List-ID: Am Mittwoch, 14. Februar 2018, 14:43:36 CET schrieb Jerome Brunet: > The orphan clocks reparents should migrate any existing count from the > orphan clock to its new acestor clocks, otherwise we may have > inconsistent counts in the tree and end-up with gated critical clocks > > Assuming we have two clocks, A and B. > * Clock A has CLK_IS_CRITICAL flag set. > * Clock B is an ancestor of A which can gate. Clock B gate is left > enabled by the bootloader. > > Step 1: Clock A is registered. Since it is a critical clock, it is > enabled. The clock being still an orphan, no parent are enabled. > > Step 2: Clock B is registered and reparented to clock A (potentially > through several other clocks). We are now in situation where the enable > count of clock A is 1 while the enable count of its ancestors is 0, which > is not good. > > Step 3: in lateinit, clk_disable_unused() is called, the enable_count of > clock B being 0, clock B is gated and and critical clock A actually gets > disabled. > > This situation was found while adding fdiv_clk gates to the meson8b > platform. These clocks parent clk81 critical clock, which is the mother > of all peripheral clocks in this system. Because of the issue described > here, the system is crashing when clk_disable_unused() is called. > > The situation is solved by reverting > commit f8f8f1d04494 ("clk: Don't touch hardware when reparenting during > registration"). To avoid breaking again the situation described in this > commit > description, enabling critical clock should be done before walking the > orphan list. This way, a parent critical clock may not be accidentally > disabled due to the CLK_OPS_PARENT_ENABLE mechanism. > > Fixes: f8f8f1d04494 ("clk: Don't touch hardware when reparenting during > registration") Cc: Stephen Boyd > Cc: Shawn Guo > Cc: Dong Aisheng > Signed-off-by: Jerome Brunet On a rk3288-veyron Chromebook Tested-by: Heiko Stuebner This made the hdmi on the machine work again with 4.16-rc1 . (hdmi-cec clock is sourced from the i2c connected pmic which provides the 32kHz clock needed) So it would be really cool if this could make it into 4.16-rc :-) Heiko