Re: [PATCH v5 3/3] counter: Add STM based counter

[Daniel Lezcano]

On 1/13/26 19:01, Frank Li wrote:
> On Tue, Jan 13, 2026 at 05:52:20PM +0100, Daniel Lezcano wrote:
> > The NXP S32G2 automotive platform integrates four Cortex-A53 cores and
> > three Cortex-M7 cores, along with a large number of timers and
> > counters. These hardware blocks can be used as clocksources or
> > clockevents, or as timestamp counters shared across the various
> > subsystems running alongside the Linux kernel, such as firmware
> > components. Their actual usage depends on the overall platform
> > software design.
> >
> > In a Linux-based system, the kernel controls the counter, which is a
> > read-only shared resource for the other subsystems. One of its primary
> > purposes is to act as a common timestamp source for messages or
> > traces, allowing correlation of events occurring in different
> > operating system contexts.
> >
> > These changes introduce a basic counter driver that can start, stop,
> > and reset the counter. It also handles overflow accounting and
> > configures the prescaler value.
> >
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> > ---

[ ... ]

> > +static int nxp_stm_cnt_count_read(struct counter_device *dev,
> > +				  struct counter_count *count, u64 *val)
> > +{
> > +	struct nxp_stm_cnt *stm_cnt = counter_priv(dev);
> > +	u32 w1, w2, cnt;
> > +
> > +	do {
> > +		w1 = atomic_read(&stm_cnt->nr_wraps);
> > +		cnt = nxp_stm_cnt_get_counter(stm_cnt);
> > +		w2 = atomic_read(&stm_cnt->nr_wraps);
> > +	} while (w1 != w2);
>
> Still have problem. Does hardware have overflow flags? This way is just
> work for hardware overflow

No, there is no overflow flag. Just a comparator.

> CPU1
>
> 	w1  = 0
>          count = 0xffff,ffff
> 	w2 = 0
>
>
> when count wrap to 0, triger irq, but irq handle have latency at CPU0,
> CPU0 have not chance to sevice irq. you can add printk at irq sevice to
> create corner case.
>
> So CPU1 get
>
> 	w1= 0
> 	count = 0
> 	w2=0
>
> so counter still suddently change to 0.

Ok, so I think I'll stick to the initial implementation and just give 
the counter number instead of trying to do fancy things.


[ ... ]

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