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sched/clock/clock_delay: added config flag to remove weak up_udelay

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While attempting to create architecture-specific implementation
of up_udelay, it was discovered that the overriding function is not
included in the final binary, the weak implementation was used instead.

Further investigation and experimentation showed that the linker
only overrides the weak implementation with the custom one if
the custom one is present in a .c source file that contains at least
one other function that is called from somewhere. Some additional
testing revealed that at least one other already present up_udelay
override (rv32m1-vega:nsh) is affected by this.

In a short mailing list discussion it was determined that this
is a likely result of using static libraries during the build process
and it was suggested to introduce configuration option that will
exclude weak implementations of the function from the build altogether.
This patch does that.

This patch does not enable this configuration option for any existing
board/chip because doing so would change its behaviour and needs
to be tested by users of the hardware.

Also changed is the static assertion in sched/clock/clock_delay.c
to not prevent building the code when architecture declares that
it does not use BOARD_LOOPSPERMSEC to determine required loop count.
BOARD_LOOPSPERMSEC is made undefined in such case.

Patch was tested by building breadxavr:nsh (identical binary by SHA256),
rv32m1-vega:nsh (identical text section) and rv-virt:nsh (text section
differs because of different ordering of functions in the binary, ostest
passed though.)

Signed-off-by: Kerogit <kr.git@kerogit.eu>
This commit is contained in:
Kerogit 2026-03-05 08:52:22 +01:00 • committed by Matteo Golin
parent a7352902ae
commit 689ed188c6
4 changed files with 122 additions and 10 deletions
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43
sched/clock/clock_delay.c
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@ -67,17 +67,27 @@
"new value to apache/nuttx."
#endif
#ifndef CONFIG_ARCH_HAVE_DYNAMIC_UDELAY
static_assert(CONFIG_BOARD_LOOPSPERMSEC != -1,
"Configure BOARD_LOOPSPERMSEC to non-default value.");
#define CONFIG_BOARD_LOOPSPER100USEC ((CONFIG_BOARD_LOOPSPERMSEC+5)/10)
#define CONFIG_BOARD_LOOPSPER10USEC ((CONFIG_BOARD_LOOPSPERMSEC+50)/100)
#define CONFIG_BOARD_LOOPSPERUSEC ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000)
/* If ARCH_HAVE_DYNAMIC_UDELAY is set, BOARD_LOOPSPERMSEC is unset,
* calculate these optionally. (Only used in udelay_coarse and
* that function is excluded from the build if these end up undefined.)
*/
# define CONFIG_BOARD_LOOPSPER100USEC ((CONFIG_BOARD_LOOPSPERMSEC+5)/10)
# define CONFIG_BOARD_LOOPSPER10USEC ((CONFIG_BOARD_LOOPSPERMSEC+50)/100)
# define CONFIG_BOARD_LOOPSPERUSEC ((CONFIG_BOARD_LOOPSPERMSEC+500)/1000)
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
#ifndef CONFIG_ARCH_HAVE_UDELAY
static void udelay_coarse(useconds_t microseconds)
{
volatile int i;
@ -125,6 +135,8 @@ static void udelay_coarse(useconds_t microseconds)
}
}
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
@ -151,13 +163,38 @@ void weak_function up_mdelay(unsigned int milliseconds)
*
* *** NOT multi-tasking friendly ***
*
* Note that this method is both marked weak and compiled optionally
* based on ARCH_HAVE_UDELAY option. This is redundant but kept
* as a temporary measure.
*
* It was discovered that sometimes the weak attribute is not enough
* to have the method replaced with other, non-weak implementation.
* (Described in more detail in help text for the ARCH_HAVE_UDELAY
* Kconfig option.) The ARCH_HAVE_UDELAY option is meant to remedy
* this but the author of the change does not own all the hardware
* that implements its own up_udelay and is affected by this problem.
*
* Enabling ARCH_HAVE_UDELAY for every such chip is therefore impossible,
* the change would be untested. Instead, the weak attribute is kept,
* preserving previous behaviour of current code. If, at some future
* time, the change is tested for other chips that implement up_udelay,
* the weak attribute and this comment can be removed.
*
* The same also applies to up_udelay implementations
* in drivers/timers/arch_alarm.c and drivers/timers/arch_timer.c
* and this comment is referenced there.
*
****************************************************************************/
#ifndef CONFIG_ARCH_HAVE_UDELAY
void weak_function up_udelay(useconds_t microseconds)
{
udelay_coarse(microseconds);
}
#endif
/****************************************************************************
* Name: up_ndelay
*