[PATCH 1/2] drivers/clocksource/fttmr010: Optimize sched_clock()

[PATCH 1/2] drivers/clocksource/fttmr010: Optimize sched_clock()

[Linus Walleij]

The sched_clock() call should be really fast so we want to
avoid an extra if() clause on the read path if possible.

Implement two sched_clock_read() functions, one if the timer
counts up and one if it counts down. Incidentally this also
mirrors how clocksource_mmio_init() works and make things
simple and easy to understand.

Suggested-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/clocksource/timer-fttmr010.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/clocksource/timer-fttmr010.c b/drivers/clocksource/timer-fttmr010.c
index f8801507a687..5e82469995cb 100644
--- a/drivers/clocksource/timer-fttmr010.c
+++ b/drivers/clocksource/timer-fttmr010.c
@@ -91,13 +91,16 @@ static inline struct fttmr010 *to_fttmr010(struct clock_event_device *evt)
 	return container_of(evt, struct fttmr010, clkevt);
 }
 
-static u64 notrace fttmr010_read_sched_clock(void)
+static u64 notrace fttmr010_read_sched_clock_up(void)
 {
-	if (local_fttmr->count_down)
-		return ~readl(local_fttmr->base + TIMER2_COUNT);
 	return readl(local_fttmr->base + TIMER2_COUNT);
 }
 
+static u64 notrace fttmr010_read_sched_clock_down(void)
+{
+	return ~readl(local_fttmr->base + TIMER2_COUNT);
+}
+
 static int fttmr010_timer_set_next_event(unsigned long cycles,
 				       struct clock_event_device *evt)
 {
@@ -304,15 +307,17 @@ static int __init fttmr010_timer_init(struct device_node *np)
 				      "FTTMR010-TIMER2",
 				      fttmr010->tick_rate,
 				      300, 32, clocksource_mmio_readl_down);
+		sched_clock_register(fttmr010_read_sched_clock_down, 32,
+				     fttmr010->tick_rate);
 	} else {
 		writel(0, fttmr010->base + TIMER2_LOAD);
 		clocksource_mmio_init(fttmr010->base + TIMER2_COUNT,
 				      "FTTMR010-TIMER2",
 				      fttmr010->tick_rate,
 				      300, 32, clocksource_mmio_readl_up);
+		sched_clock_register(fttmr010_read_sched_clock_up, 32,
+				     fttmr010->tick_rate);
 	}
-	sched_clock_register(fttmr010_read_sched_clock, 32,
-			     fttmr010->tick_rate);
 
 	/*
 	 * Setup clockevent timer (interrupt-driven) on timer 1.
-- 
2.9.4

[PATCH 2/2] drivers/clocksource/fttmr010: Implement delay timer

[Linus Walleij]

This timer is often used on the ARM architecture, so as with so
many siblings, we can implement delay timers, removing the need
for the system to calibrate jiffys at boot, and potentially
handling CPU frequency scaling on targets.

We cannot just protect the Kconfig with a "depends on ARM" because
it is already known that different architectures are using Faraday
IP blocks, so it is better to make things open-ended and use

Result on boot dmesg:

Switching to timer-based delay loop, resolution 40n
Calibrating delay loop (skipped), value calculated using
  timer frequency.. 50.00 BogoMIPS (lpj=250000)

This is accurately the timer frequency, 250MHz on the APB
bus.

Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/clocksource/timer-fttmr010.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-fttmr010.c b/drivers/clocksource/timer-fttmr010.c
index 5e82469995cb..0074d89cd2ce 100644
--- a/drivers/clocksource/timer-fttmr010.c
+++ b/drivers/clocksource/timer-fttmr010.c
@@ -17,6 +17,7 @@
 #include <linux/clk.h>
 #include <linux/slab.h>
 #include <linux/bitops.h>
+#include <linux/delay.h>
 
 /*
  * Register definitions for the timers
@@ -81,9 +82,15 @@ struct fttmr010 {
 	bool count_down;
 	u32 t1_enable_val;
 	struct clock_event_device clkevt;
+#ifdef CONFIG_ARM
+	struct delay_timer delay_timer;
+#endif
 };
 
-/* A local singleton used by sched_clock, which is stateless */
+/*
+ * A local singleton used by sched_clock and delay timer reads, which are
+ * fast and stateless
+ */
 static struct fttmr010 *local_fttmr;
 
 static inline struct fttmr010 *to_fttmr010(struct clock_event_device *evt)
@@ -101,6 +108,20 @@ static u64 notrace fttmr010_read_sched_clock_down(void)
 	return ~readl(local_fttmr->base + TIMER2_COUNT);
 }
 
+#ifdef CONFIG_ARM
+
+static unsigned long fttmr010_read_current_timer_up(void)
+{
+	return readl(local_fttmr->base + TIMER2_COUNT);
+}
+
+static unsigned long fttmr010_read_current_timer_down(void)
+{
+	return ~readl(local_fttmr->base + TIMER2_COUNT);
+}
+
+#endif
+
 static int fttmr010_timer_set_next_event(unsigned long cycles,
 				       struct clock_event_device *evt)
 {
@@ -349,6 +370,18 @@ static int __init fttmr010_timer_init(struct device_node *np)
 					fttmr010->tick_rate,
 					1, 0xffffffff);
 
+#ifdef CONFIG_ARM
+	/* Also use this timer for delays */
+	if (fttmr010->count_down)
+		fttmr010->delay_timer.read_current_timer =
+			fttmr010_read_current_timer_down;
+	else
+		fttmr010->delay_timer.read_current_timer =
+			fttmr010_read_current_timer_up;
+	fttmr010->delay_timer.freq = fttmr010->tick_rate;
+	register_current_timer_delay(&fttmr010->delay_timer);
+#endif
+
 	return 0;
 
 out_unmap:
-- 
2.9.4

Re: [PATCH 2/2] drivers/clocksource/fttmr010: Implement delay timer

[Daniel Lezcano]

On Sun, Jun 11, 2017 at 11:26:17PM +0200, Linus Walleij wrote:
> This timer is often used on the ARM architecture, so as with so
> many siblings, we can implement delay timers, removing the need
> for the system to calibrate jiffys at boot, and potentially
> handling CPU frequency scaling on targets.
> 
> We cannot just protect the Kconfig with a "depends on ARM" because
> it is already known that different architectures are using Faraday
> IP blocks, so it is better to make things open-ended and use
> 
> Result on boot dmesg:
> 
> Switching to timer-based delay loop, resolution 40n
> Calibrating delay loop (skipped), value calculated using
>   timer frequency.. 50.00 BogoMIPS (lpj=250000)
> 
> This is accurately the timer frequency, 250MHz on the APB
> bus.
> 
> Cc: Andrew Jeffery <andrew@aj.id.au>
> Cc: Joel Stanley <joel@jms.id.au>
> Cc: Jonas Jensen <jonas.jensen@gmail.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>  drivers/clocksource/timer-fttmr010.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/timer-fttmr010.c b/drivers/clocksource/timer-fttmr010.c
> index 5e82469995cb..0074d89cd2ce 100644
> --- a/drivers/clocksource/timer-fttmr010.c
> +++ b/drivers/clocksource/timer-fttmr010.c
> @@ -17,6 +17,7 @@
>  #include <linux/clk.h>
>  #include <linux/slab.h>
>  #include <linux/bitops.h>
> +#include <linux/delay.h>
>  
>  /*
>   * Register definitions for the timers
> @@ -81,9 +82,15 @@ struct fttmr010 {
>  	bool count_down;
>  	u32 t1_enable_val;
>  	struct clock_event_device clkevt;
> +#ifdef CONFIG_ARM
> +	struct delay_timer delay_timer;
> +#endif
>  };
>  
> -/* A local singleton used by sched_clock, which is stateless */
> +/*
> + * A local singleton used by sched_clock and delay timer reads, which are
> + * fast and stateless
> + */
>  static struct fttmr010 *local_fttmr;
>  
>  static inline struct fttmr010 *to_fttmr010(struct clock_event_device *evt)
> @@ -101,6 +108,20 @@ static u64 notrace fttmr010_read_sched_clock_down(void)
>  	return ~readl(local_fttmr->base + TIMER2_COUNT);
>  }
>  
> +#ifdef CONFIG_ARM
> +
> +static unsigned long fttmr010_read_current_timer_up(void)
> +{
> +	return readl(local_fttmr->base + TIMER2_COUNT);
> +}
> +
> +static unsigned long fttmr010_read_current_timer_down(void)
> +{
> +	return ~readl(local_fttmr->base + TIMER2_COUNT);
> +}
> +
> +#endif
> +

These functions are duplicated with fttmr010_read_sched_clock_down() /
fttmr010_read_sched_clock_up().

Could you factor them out?

eg.

static inline unsigned long fttmr010_read_current_timer_up(void)
{
	return readl(local_fttmr->base + TIMER2_COUNT);
}

static inline unsigned long fttmr010_read_current_timer_down(void)
{
	return ~readl(local_fttmr->base + TIMER2_COUNT);
}

static u64 notrace fttmr010_read_sched_clock_down(void)
{
	return fttmr010_read_current_timer_down()
}

static u64 notrace fttmr010_read_sched_clock_up(void)
{
	return fttmr010_read_current_timer_up();
}

So we get rid of these CONFIG_ARM section above.

>  static int fttmr010_timer_set_next_event(unsigned long cycles,
>  				       struct clock_event_device *evt)
>  {
> @@ -349,6 +370,18 @@ static int __init fttmr010_timer_init(struct device_node *np)
>  					fttmr010->tick_rate,
>  					1, 0xffffffff);
>  
> +#ifdef CONFIG_ARM
> +	/* Also use this timer for delays */
> +	if (fttmr010->count_down)
> +		fttmr010->delay_timer.read_current_timer =
> +			fttmr010_read_current_timer_down;
> +	else
> +		fttmr010->delay_timer.read_current_timer =
> +			fttmr010_read_current_timer_up;
> +	fttmr010->delay_timer.freq = fttmr010->tick_rate;
> +	register_current_timer_delay(&fttmr010->delay_timer);
> +#endif
> +
>  	return 0;
>  
>  out_unmap:
> -- 
> 2.9.4
> 

-- 

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Re: [PATCH 2/2] drivers/clocksource/fttmr010: Implement delay timer

[Jonas Jensen]

On 11 June 2017 at 23:26, Linus Walleij <linus.walleij@linaro.org> wrote:
> Switching to timer-based delay loop, resolution 40n
> Calibrating delay loop (skipped), value calculated using
>   timer frequency.. 50.00 BogoMIPS (lpj=250000)

Thanks for this, these work OK on UC-7112-LX.

I stumbled upon boot time savings (going from next-20170518 to
next-20170609) which seem to shave off more than a second ([1]
compared to [2]) so I also booted without patches ([3]).
There seems to be improvement when these patches are applied.

[1] https://bitbucket.org/Kasreyn/linux-next/commits/ceb7a070629807ed62c1101603655bebdbec5204
Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.12.0-rc4-next-20170609-00005-gceb7a07
(i@ildjarn) (gcc version 4.9.1 (crosstool-NG 1.20.0) ) #4549 PREEMPT
Mon Jun 12 13:04:19 CEST 2017
[    0.000000] CPU: FA526 [66015261] revision 1 (ARMv4), cr=0000397f
[    0.000000] CPU: VIVT data cache, VIVT instruction cache
[    0.000000] OF: fdt: Machine model: MOXA UC-7112-LX
[    0.000000] bootconsole [earlycon0] enabled
[    0.000000] Memory policy: Data cache writeback
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.
Total pages: 8128
[    0.000000] Kernel command line: console=ttyS0,115200n8 earlyprintk
root=/dev/mmcblk0p1 rw rootwait
[    0.000000] PID hash table entries: 128 (order: -3, 512 bytes)
[    0.000000] Dentry cache hash table entries: 4096 (order: 2, 16384 bytes)
[    0.000000] Inode-cache hash table entries: 2048 (order: 1, 8192 bytes)
[    0.000000] Memory: 25816K/32768K available (4096K kernel code,
112K rwdata, 668K rodata, 1024K init, 288K bss, 6952K reserved, 0K
cma-reserved)
[    0.000000] Virtual kernel memory layout:
[    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
[    0.000000]     fixmap  : 0xffc00000 - 0xfff00000   (3072 kB)
[    0.000000]     vmalloc : 0xc2800000 - 0xff800000   ( 976 MB)
[    0.000000]     lowmem  : 0xc0000000 - 0xc2000000   (  32 MB)
[    0.000000]       .text : 0xc0008000 - 0xc0500000   (5088 kB)
[    0.000000]       .init : 0xc0600000 - 0xc0700000   (1024 kB)
[    0.000000]       .data : 0xc0700000 - 0xc071c2a0   ( 113 kB)
[    0.000000]        .bss : 0xc0720674 - 0xc0768780   ( 289 kB)
[    0.000000] SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
[    0.000000] Preemptible hierarchical RCU implementation.
[    0.000000]  Tasks RCU enabled.
[    0.000000] NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16
[    0.000000] clocksource: FTTMR010-TIMER2: mask: 0xffffffff
max_cycles: 0xffffffff, max_idle_ns: 39817925974 ns
[    0.000062] sched_clock: 32 bits at 48MHz, resolution 20ns, wraps
every 44739242997ns
[    0.008405] Switching to timer-based delay loop, resolution 20ns
[    0.021091] kmemleak: Kernel memory leak detector disabled
[    0.031970] kmemleak: Early log buffer exceeded (1229), please
increase DEBUG_KMEMLEAK_EARLY_LOG_SIZE
[    0.041868] Calibrating delay loop (skipped), value calculated
using timer frequency.. 96.00 BogoMIPS (lpj=480000)
[    0.052806] pid_max: default: 4096 minimum: 301
[    0.058925] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.066022] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.077057] CPU: Testing write buffer coherency: ok
[    0.090239] Setting up static identity map for 0x100000 - 0x100048
[    0.097927] Hierarchical SRCU implementation.
[    0.141643] devtmpfs: initialized
[    0.172834] DMA-API: preallocated 4096 debug entries
[    0.178088] DMA-API: debugging enabled by kernel config
[    0.185933] clocksource: jiffies: mask: 0xffffffff max_cycles:
0xffffffff, max_idle_ns: 19112604462750000 ns
[    0.198365] kworker/u2:0 (13) used greatest stack depth: 6732 bytes left
[    0.206072] futex hash table entries: 16 (order: -5, 192 bytes)
[    0.215797] random: bucket_table_alloc+0x94/0x248 get_random_u32
called with crng_init=0
[    0.226839] NET: Registered protocol family 16
[    0.242597] DMA: preallocated 256 KiB pool for atomic coherent allocations
[    0.286674] kworker/u2:1 (25) used greatest stack depth: 6476 bytes left
[    0.554111] clocksource: Switched to clocksource FTTMR010-TIMER2
[    0.592605] NET: Registered protocol family 2
[    0.600601] random: neigh_hash_alloc+0x9c/0xe4 get_random_u32
called with crng_init=0
[    0.613871] random: rt_genid_init+0x18/0x28 get_random_u32 called
with crng_init=0
[    0.623192] TCP established hash table entries: 1024 (order: 0, 4096 bytes)
[    0.631215] TCP bind hash table entries: 1024 (order: 0, 4096 bytes)
[    0.638463] TCP: Hash tables configured (established 1024 bind 1024)
[    0.646917] UDP hash table entries: 256 (order: 0, 4096 bytes)
[    0.653246] UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
[    0.661388] NET: Registered protocol family 1
[    0.684891] workingset: timestamp_bits=30 max_order=13 bucket_order=0
[    0.847527] kworker/u2:1 (202) used greatest stack depth: 6452 bytes left
[    0.889185] jffs2: version 2.2. (NAND) © 2001-2006 Red Hat, Inc.
[    0.947029] io scheduler noop registered
[    0.955454] io scheduler cfq registered (default)
[    0.960470] io scheduler mq-deadline registered
[    0.966328] io scheduler kyber registered
[    0.986690] ftgpio010-gpio 98700000.gpio: FTGPIO010 @c289e000 registered
[    1.006881] Serial: 8250/16550 driver, 1 ports, IRQ sharing enabled
[    1.028261] console [ttyS0] disabled
[    1.033357] 98200000.uart: ttyS0 at MMIO 0x98200000 (irq = 21,
base_baud = 921600) is a 16550A
[    1.043679] console [ttyS0] enabled
[    1.043679] console [ttyS0] enabled
[    1.051850] bootconsole [earlycon0] disabled
[    1.051850] bootconsole [earlycon0] disabled
[    1.101640] 80000000.flash: Found 1 x16 devices at 0x0 in 16-bit
bank. Manufacturer ID 0x000089 Chip ID 0x000018
[    1.112766] Intel/Sharp Extended Query Table at 0x0031
[    1.118581] Intel/Sharp Extended Query Table at 0x0031
[    1.123882] Using buffer write method
[    1.128057] cfi_cmdset_0001: Erase suspend on write enabled
[    1.134012] 4 ofpart partitions found on MTD device 80000000.flash
[    1.140561] Creating 4 MTD partitions on "80000000.flash":
[    1.146468] 0x000000000000-0x000000040000 : "bootloader"
[    1.168490] 0x000000040000-0x000000200000 : "linux kernel"
[    1.192265] 0x000000200000-0x000000a00000 : "root filesystem"
[    1.217379] 0x000000a00000-0x000001000000 : "user filesystem"
[    1.890595] libphy: MOXA ART Ethernet MII: probed
[    2.554143] random: fast init done
[    2.565768] libphy: MOXA ART Ethernet MII: probed
[    2.599346] libphy: Fixed MDIO Bus: probed
[    2.649311] moxart-rtc 90000000.soc:rtc: rtc core: registered
90000000.soc:rtc as rtc0
[    2.680285] sdhci: Secure Digital Host Controller Interface driver
[    2.689336] sdhci: Copyright(c) Pierre Ossman
[    2.764421] sdhci-pltfm: SDHCI platform and OF driver helper
[    2.786042] NET: Registered protocol family 17
[    2.814928] mmc0: new SDHC card at address e624
[    2.822331] console [netcon0] enabled
[    2.828128] netconsole: network logging started
[    2.839709] mmcblk0: mmc0:e624 SS04G 3.69 GiB
[    2.848309] moxart-rtc 90000000.soc:rtc: setting system clock to
2017-06-12 11:15:23 UTC (1497266123)
[    2.865883]  mmcblk0: p1
[    2.885535] EXT4-fs (mmcblk0p1): mounting ext3 file system using
the ext4 subsystem
[    4.168117] EXT4-fs (mmcblk0p1): recovery complete
[    4.178633] EXT4-fs (mmcblk0p1): mounted filesystem with ordered
data mode. Opts: (null)
[    4.187497] VFS: Mounted root (ext3 filesystem) on device 179:1.
[    4.226905] devtmpfs: mounted
[    4.298371] Freeing unused kernel memory: 1024K
INIT: version 2.88 booting

[2] https://bitbucket.org/Kasreyn/linux-next/commits/78456248df9eeb48c963b574f50c7268713ef0b1
Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.12.0-rc1-next-20170518-00010-g7845624
(i@ildjarn) (gcc version 4.9.1 (crosstool-NG 1.20.0) ) #4486 PREEMPT
Fri May 19 14:04:54 CEST 2017
..
[    2.543134] 4 ofpart partitions found on MTD device 80000000.flash
[    2.550035] Creating 4 MTD partitions on "80000000.flash":
[    2.555941] 0x000000000000-0x000000040000 : "bootloader"
[    2.563134] random: fast init done
[    2.634452] 0x000000040000-0x000000200000 : "linux kernel"
[    2.686438] 0x000000200000-0x000000a00000 : "root filesystem"
[    2.744918] 0x000000a00000-0x000001000000 : "user filesystem"

[3] https://bitbucket.org/Kasreyn/linux-next/commits/75a5fce74de4172fb6ce32aa1f4e208657013006
Uncompressing Linux... done, booting the kernel.
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.12.0-rc4-next-20170609-00003-g75a5fce
(i@ildjarn) (gcc version 4.9.1 (crosstool-NG 1.20.0) ) #4550 PREEMPT
Mon Jun 12 13:58:32 CEST 2017
..
[    1.185855] 4 ofpart partitions found on MTD device 80000000.flash
[    1.192166] Creating 4 MTD partitions on "80000000.flash":
[    1.198093] 0x000000000000-0x000000040000 : "bootloader"
[    1.220088] 0x000000040000-0x000000200000 : "linux kernel"
[    1.244496] 0x000000200000-0x000000a00000 : "root filesystem"
[    1.269177] 0x000000a00000-0x000001000000 : "user filesystem"


Tested-by: Jonas Jensen <jonas.jensen@gmail.com>

Re: [PATCH 2/2] drivers/clocksource/fttmr010: Implement delay timer

[Andrew Jeffery]

[-- Attachment #1: Type: text/plain, Size: 3468 bytes --]

On Sun, 2017-06-11 at 23:26 +0200, Linus Walleij wrote:
> This timer is often used on the ARM architecture, so as with so
> many siblings, we can implement delay timers, removing the need
> for the system to calibrate jiffys at boot, and potentially
> handling CPU frequency scaling on targets.
> 
> We cannot just protect the Kconfig with a "depends on ARM" because
> it is already known that different architectures are using Faraday
> IP blocks, so it is better to make things open-ended and use

Seems like we're missing the end of the sentence?

> 
> Result on boot dmesg:
> 
> Switching to timer-based delay loop, resolution 40n
> Calibrating delay loop (skipped), value calculated using
>   timer frequency.. 50.00 BogoMIPS (lpj=250000)
> 
> This is accurately the timer frequency, 250MHz on the APB
> bus.
> 
> > Cc: Andrew Jeffery <andrew@aj.id.au>
> > Cc: Joel Stanley <joel@jms.id.au>
> > Cc: Jonas Jensen <jonas.jensen@gmail.com>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Tried both patches on an AST2500, everything worked as suggested.

Tested-by: Andrew Jeffery <andrew@aj.id.au>

> ---
>  drivers/clocksource/timer-fttmr010.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clocksource/timer-fttmr010.c b/drivers/clocksource/timer-fttmr010.c
> index 5e82469995cb..0074d89cd2ce 100644
> --- a/drivers/clocksource/timer-fttmr010.c
> +++ b/drivers/clocksource/timer-fttmr010.c
> @@ -17,6 +17,7 @@
>  #include <linux/clk.h>
>  #include <linux/slab.h>
>  #include <linux/bitops.h>
> +#include <linux/delay.h>
>  
>  /*
>   * Register definitions for the timers
> @@ -81,9 +82,15 @@ struct fttmr010 {
> >  	bool count_down;
> >  	u32 t1_enable_val;
> >  	struct clock_event_device clkevt;
> +#ifdef CONFIG_ARM
> > +	struct delay_timer delay_timer;
> +#endif
>  };
>  
> -/* A local singleton used by sched_clock, which is stateless */
> +/*
> + * A local singleton used by sched_clock and delay timer reads, which are
> + * fast and stateless
> + */
>  static struct fttmr010 *local_fttmr;
>  
>  static inline struct fttmr010 *to_fttmr010(struct clock_event_device *evt)
> @@ -101,6 +108,20 @@ static u64 notrace fttmr010_read_sched_clock_down(void)
> >  	return ~readl(local_fttmr->base + TIMER2_COUNT);
>  }
>  
> +#ifdef CONFIG_ARM
> +
> +static unsigned long fttmr010_read_current_timer_up(void)
> +{
> > +	return readl(local_fttmr->base + TIMER2_COUNT);
> +}
> +
> +static unsigned long fttmr010_read_current_timer_down(void)
> +{
> > +	return ~readl(local_fttmr->base + TIMER2_COUNT);
> +}
> +
> +#endif
> +
>  static int fttmr010_timer_set_next_event(unsigned long cycles,
> >  				       struct clock_event_device *evt)
>  {
> @@ -349,6 +370,18 @@ static int __init fttmr010_timer_init(struct device_node *np)
> >  					fttmr010->tick_rate,
> >  					1, 0xffffffff);
>  
> +#ifdef CONFIG_ARM
> > +	/* Also use this timer for delays */
> > +	if (fttmr010->count_down)
> > +		fttmr010->delay_timer.read_current_timer =
> > +			fttmr010_read_current_timer_down;
> > +	else
> > +		fttmr010->delay_timer.read_current_timer =
> > +			fttmr010_read_current_timer_up;
> > +	fttmr010->delay_timer.freq = fttmr010->tick_rate;
> > +	register_current_timer_delay(&fttmr010->delay_timer);
> +#endif
> +
> >  	return 0;
>  
>  out_unmap:

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Re: [PATCH 2/2] drivers/clocksource/fttmr010: Implement delay timer

[Linus Walleij]

On Mon, Jun 12, 2017 at 2:41 PM, Jonas Jensen <jonas.jensen@gmail.com> wrote:

> I stumbled upon boot time savings (going from next-20170518 to
> next-20170609) which seem to shave off more than a second ([1]
> compared to [2]) so I also booted without patches ([3]).
> There seems to be improvement when these patches are applied.

Oh yes, using delay timers saves us the loop calibration time.

Actually I should mention that, it's pretty nice.

Thanks for testing!

Yours,
Linus Walleij