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logging: swo: add Kconfig option for SWO reference frequency

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SWO reference frequency was set based on `swo-ref-frequency` under `itm`
nodelabel or `/cpus/cpu@0/clock-frequency` property. Not all platforms
configure those.

All ST devices configure CPU frequency in `clock-frequency` under `rcc`
nodelabel. Configuring the same value for each board in
`/cpus/cpu@0/clock-frequency` would be one way to make SWO work out of the
box. There is lots of copy-pasting involved in this, which makes this very
error-prone.

Introduce Kconfig option, which will default to values configured in `itm`
or `/cpus/cpu@0`. The main advantage will be for platforms like ST, where
CPU clock frequency is already configured in another place. Thsoe could
override default value in SoC, board or any other platform specific layer.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>
This commit is contained in:
Marcin Niestroj 2023-08-03 21:13:52 +02:00 • committed by Carles Cufí
commit a9fbcd2785
2 changed files with 13 additions and 8 deletions
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10
subsys/logging/backends/Kconfig.swo
View file

@ -9,6 +9,16 @@ config LOG_BACKEND_SWO
When enabled, backend will use SWO for logging.
if LOG_BACKEND_SWO
config LOG_BACKEND_SWO_REF_FREQ_HZ
int "SWO reference clock frequency"
default $(dt_node_int_prop_int,$(dt_nodelabel_path,itm),swo-ref-frequency) if $(dt_nodelabel_enabled,itm)
default $(dt_node_int_prop_int,/cpus/cpu@0,clock-frequency) if $(dt_node_has_prop,/cpus/cpu@0,clock-frequency)
default 0
help
Set SWO reference frequency. In most cases it is equal to CPU
frequency.
config LOG_BACKEND_SWO_FREQ_HZ
int "Set SWO output frequency"
default 0

11
subsys/logging/backends/log_backend_swo.c
View file

@ -42,17 +42,12 @@ PINCTRL_DT_DEFINE(DT_NODELABEL(itm));
#define SWO_FREQ_DIV 1
#else
/* Set reference frequency which can be custom or cpu frequency. */
#if DT_NODE_HAS_PROP(DT_NODELABEL(itm), swo_ref_frequency)
#define SWO_REF_FREQ DT_PROP(DT_NODELABEL(itm), swo_ref_frequency)
#elif DT_NODE_HAS_PROP(DT_PATH(cpus, cpu_0), clock_frequency)
#define SWO_REF_FREQ DT_PROP(DT_PATH(cpus, cpu_0), clock_frequency)
#else
#error "Missing DT 'clock-frequency' property on cpu@0 node"
#if CONFIG_LOG_BACKEND_SWO_REF_FREQ_HZ == 0
#error "SWO reference frequency is not configured"
#endif
#define SWO_FREQ_DIV \
((SWO_REF_FREQ + (CONFIG_LOG_BACKEND_SWO_FREQ_HZ / 2)) / \
((CONFIG_LOG_BACKEND_SWO_REF_FREQ_HZ + (CONFIG_LOG_BACKEND_SWO_FREQ_HZ / 2)) / \
CONFIG_LOG_BACKEND_SWO_FREQ_HZ)
#if SWO_FREQ_DIV > 0xFFFF