From 4c8a7b80d5f3c924fbe08b24634fb67a97f96465 Mon Sep 17 00:00:00 2001 From: Alexander Stein Date: Wed, 13 Oct 2021 09:49:54 +0200 Subject: [PATCH] rtc: pcf85063: add support for fixed clock TQ-Systems' TQMa8Mx module (SoM) uses a pcf85063 as RTC. The default output is 32768Hz. This is to provide the i.MX8M CKIL clock. Once the RTC driver is probed, the clock is disabled and all i.MX8M functionality depending on the 32 KHz clock will halt. In our case the whole system halts and a power cycle is required. Referencing the pcf85063 directly results in a deadlock. The kernel will see, that i.MX8M system clock needs the RTC clock and do probe deferral. But the i.MX8M I2C module never becomes usable without the i.MX8M CKIL clock and thus the RTC's clock will not be probed. So from the kernel's perspective this is a chicken-and-egg problem. Technically everything is fine by not touching anything, since the RTC clock correctly enables the clock on reset (i.e. on battery backup power loss). A workaround for this issue is describing the square wave pin as fixed-clock, which is registered early and basically how this pin is used on the i.MX8M. This addresses the exact same issue as in commit f765e349c3e1 ("rtc: m41t80: add support for fixed clock"). Signed-off-by: Alexander Stein Reported-by: kernel test robot Signed-off-by: Alexandre Belloni [Fixed return value 0 -> NULL] Link: https://lore.kernel.org/r/20211013074954.997445-1-alexander.stein@ew.tq-group.com --- Documentation/devicetree/bindings/rtc/nxp,pcf85063.txt | 9 +++++++++ drivers/rtc/rtc-pcf85063.c | 12 ++++++++++++ 2 files changed, 21 insertions(+) diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf85063.txt b/Documentation/devicetree/bindings/rtc/nxp,pcf85063.txt index 627bb53..6439682 100644 --- a/Documentation/devicetree/bindings/rtc/nxp,pcf85063.txt +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf85063.txt @@ -13,10 +13,19 @@ Optional property: expressed in femto Farad (fF). Valid values are 7000 and 12500. Default value (if no value is specified) is 7000fF. +Optional child node: +- clock: Provide this if the square wave pin is used as boot-enabled fixed clock. + Example: pcf85063: rtc@51 { compatible = "nxp,pcf85063"; reg = <0x51>; quartz-load-femtofarads = <12500>; + + clock { + compatible = "fixed-clock"; + #clock-cells = <0>; + clock-frequency = <32768>; + }; }; diff --git a/drivers/rtc/rtc-pcf85063.c b/drivers/rtc/rtc-pcf85063.c index 14da4ab..3e59590f 100644 --- a/drivers/rtc/rtc-pcf85063.c +++ b/drivers/rtc/rtc-pcf85063.c @@ -479,6 +479,18 @@ static struct clk *pcf85063_clkout_register_clk(struct pcf85063 *pcf85063) struct clk *clk; struct clk_init_data init; struct device_node *node = pcf85063->rtc->dev.parent->of_node; + struct device_node *fixed_clock; + + fixed_clock = of_get_child_by_name(node, "clock"); + if (fixed_clock) { + /* + * skip registering square wave clock when a fixed + * clock has been registered. The fixed clock is + * registered automatically when being referenced. + */ + of_node_put(fixed_clock); + return NULL; + } init.name = "pcf85063-clkout"; init.ops = &pcf85063_clkout_ops; -- 2.7.4