On 13.11.23 14:03, Sascha Hauer wrote: > On Thu, Nov 09, 2023 at 12:47:06PM +0100, Ahmad Fatoum wrote: >> From: Ahmad Fatoum <ah...@a3f.at> >> >> clk_get will return -EPROBE_DEFER if clock provider hasn't yet been >> probed. In a system with deep probe enabled, dependencies are probed >> on demand, so a -EPROBE_DEFER return is final and the console probe >> will never succeed. >> >> CONFIG_DEBUG_LL is often used to debug this, but because the low-level >> console is not interactive, it's a bit cumbersome. Improve upon this a >> bit, by providing a clk_get_for_console helper that returns NULL if and >> only if we are sure that a clock provider will not be probed. >> >> In that case, the driver can skip code paths initialization code and >> baud rate setting dependent on having access to the clock and still >> register a console that reuses what was set up by CONFIG_DEBUG_LL. >> >> Signed-off-by: Ahmad Fatoum <ah...@a3f.at> >> --- >> include/console.h | 26 ++++++++++++++++++++++++++ >> include/linux/clk.h | 21 +++++++++++++++++++++ >> 2 files changed, 47 insertions(+) >> >> diff --git a/include/console.h b/include/console.h >> index 586b68f73301..b8c901801e9f 100644 >> --- a/include/console.h >> +++ b/include/console.h >> @@ -8,6 +8,7 @@ >> #define _CONSOLE_H_ >> >> #include <param.h> >> +#include <linux/clk.h> >> #include <linux/list.h> >> #include <driver.h> >> #include <serdev.h> >> @@ -208,4 +209,29 @@ static inline void console_ctrlc_allow(void) { } >> static inline void console_ctrlc_forbid(void) { } >> #endif >> >> +/** >> + * clk_get_for_console - get clock, ignoring known unavailable clock >> controller >> + * @dev: device for clock "consumer" >> + * @id: clock consumer ID >> + * >> + * Return: a struct clk corresponding to the clock producer, a >> + * valid IS_ERR() condition containing errno or NULL if it could >> + * be determined that the clock producer will never be probed in >> + * absence of modules. The NULL return allows serial drivers to >> + * skip clock handling and rely on CONFIG_DEBUG_LL. >> + */ >> +static inline struct clk *clk_get_for_console(struct device *dev, const >> char *id) >> +{ >> + struct clk *clk; >> + >> + if (!IS_ENABLED(CONFIG_DEBUG_LL)) >> + return clk_get(dev, id); > > There are several SoCs out there where the UART is enabled by the ROM > already, on these we don't need to have CONFIG_DEBUG_LL enabled for a > working UART.
Those SoCs can still implement CONFIG_DEBUG_LL and just skip the initialization step. > Maybe testing for the UART enable bit in probe() would be a better > indication that the UART is already in a working state? If clk turns out to be not enabled, system would hang on e.g. i.MX. This is a mere debugging measure for SoCs with complex clock controllers backed by firmware, so I think having to enable CONFIG_DEBUG_LL to use is acceptable. Cheers, Ahmad > > Sascha > >> + >> + clk = clk_get_if_available(dev, id); >> + if (clk == NULL) >> + dev_warn(dev, "couldn't get clock (ignoring)\n"); >> + >> + return clk; >> +} >> + >> #endif >> diff --git a/include/linux/clk.h b/include/linux/clk.h >> index 61b4ff3127cf..f505f18a75c0 100644 >> --- a/include/linux/clk.h >> +++ b/include/linux/clk.h >> @@ -14,6 +14,7 @@ >> #include <linux/spinlock.h> >> #include <linux/stringify.h> >> #include <linux/container_of.h> >> +#include <deep-probe.h> >> #include <xfuncs.h> >> >> struct device; >> @@ -982,4 +983,24 @@ static inline struct clk *clk_get_enabled(struct device >> *dev, const char *id) >> return clk; >> } >> >> +/** >> + * clk_get_if_available - get clock, ignoring known unavailable clock >> controller >> + * @dev: device for clock "consumer" >> + * @id: clock consumer ID >> + * >> + * Return: a struct clk corresponding to the clock producer, a >> + * valid IS_ERR() condition containing errno or NULL if it could >> + * be determined that the clock producer will never be probed in >> + * absence of modules. >> + */ >> +static inline struct clk *clk_get_if_available(struct device *dev, const >> char *id) >> +{ >> + struct clk *clk = clk_get(dev, id); >> + >> + if (clk == ERR_PTR(-EPROBE_DEFER) && deep_probe_is_supported()) >> + return NULL; >> + >> + return clk; >> +} >> + >> #endif >> -- >> 2.39.2 >> >> >> > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |