On Mon, 12 Nov 2018, Geert Uytterhoeven wrote:
Hi Finn,
On Mon, Nov 12, 2018 at 5:46 AM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
Add a platform clocksource by adapting the existing arch_gettimeoffset
implementation.
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
Thanks for your patch!
Thanks for your review.
--- a/arch/m68k/amiga/config.c
+++ b/arch/m68k/amiga/config.c
@@ -17,6 +17,7 @@
#include <linux/mm.h>
#include <linux/seq_file.h>
#include <linux/tty.h>
+#include <linux/clocksource.h>
#include <linux/console.h>
#include <linux/rtc.h>
#include <linux/init.h>
@@ -461,7 +462,30 @@ void __init config_amiga(void)
*(unsigned char *)ZTWO_VADDR(0xde0002) |= 0x80;
}
+static u64 amiga_read_clk(struct clocksource *cs);
+
+static struct clocksource amiga_clk = {
+ .name = "ciab",
+ .rating = 250,
+ .read = amiga_read_clk,
+ .mask = CLOCKSOURCE_MASK(32),
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
static unsigned short jiffy_ticks;
+static u32 clk_total;
Shouldn't clk_total be u64?
Well, it was intentionally u32, and amiga_clk.mask was intentionally
CLOCKSOURCE_MASK(32)...
+
+static irqreturn_t ciab_timer_handler(int irq, void *data)
+{
+ irq_handler_t timer_routine = data;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ clk_total += jiffy_ticks;
+ local_irq_restore(flags);
+
+ return timer_routine(irq, data);
+}
[...]
-static u32 amiga_gettimeoffset(void)
+static u64 amiga_read_clk(struct clocksource *cs)
{
unsigned long flags;
unsigned short hi, lo, hi2;
@@ -512,14 +537,13 @@ static u32 amiga_gettimeoffset(void)
if (ticks > jiffy_ticks / 2)
/* check for pending interrupt */
if (cia_set_irq(&ciab_base, 0) & CIA_ICR_TA)
- offset = 10000;
+ offset = jiffy_ticks;
local_irq_restore(flags);
ticks = jiffy_ticks - ticks;
- ticks = (10000 * ticks) / jiffy_ticks;
- return (ticks + offset) * 1000;
+ return clk_total + ticks + offset;
... to return a full 64-bit value here?
It's certainly possible. Is it better? It sounds like a question about the
cost of wrap-around in the clocksource core vs. the cost of 64-bit
additions in the arch code.
Looking at __clocksource_update_freq_scale() there are some consequences
to choosing a 32-bit mask --
* For clocksources which have a mask > 32-bit
* we need to limit the max sleep time to have a good
* conversion precision.
I don't know the answer, sorry.
--
Gr{oetje,eeting}s,
Geert
