lkml.org 
[lkml]   [2018]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] clocksource: arc_timer: add comments about locking while read GFRC
From
Date
On 04/17/2018 08:52 AM, Eugeniy Paltsev wrote:
> This came to light in some internal discussions and it is nice to have
> this documented rather than digging up the PRM (Prog Ref Manual) again.
>
> Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>

Minor nits below, otherwise LGTM !
Acked-by: Vineet Gupta <vgupta@synopsys.com>

> ---
> drivers/clocksource/arc_timer.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/clocksource/arc_timer.c b/drivers/clocksource/arc_timer.c
> index 4927355f9cbe..b594c373debc 100644
> --- a/drivers/clocksource/arc_timer.c
> +++ b/drivers/clocksource/arc_timer.c
> @@ -61,6 +61,19 @@ static u64 arc_read_gfrc(struct clocksource *cs)
> unsigned long flags;
> u32 l, h;
>
> + /*
> + * MCIP_CMD/MCIP_READBACK registers are allocated

From a programming model pov, there seems to be just one instance of
MCIP_CMD/MCIP_READBACK however micro-architecturally there's an instance PER ARC
CORE.....
> + * PER ARC CORE (not per cluster), and there are dedicated hardware
> + * decode logic (per core) inside ARConnect to handle simultaneous
> + * read/write accesses from cores via those two registers.
> + * So several concurrent commands to ARConnect are OK if they are
> + * trying to access two different sub-components (like GFRC,
> + * inter-core interrupt, etc...). HW also support simultaneously

s/support/supports/

> + * accessing GFRC by multiple cores.
> + * That's why it is safe to disable hard interrupts on the local CPU
> + * before access to GFRC instead of taking global MCIP spinlock
> + * defined in arch/arc/kernel/mcip.c
> + */
> local_irq_save(flags);
>
> __mcip_cmd(CMD_GFRC_READ_LO, 0);

\
 
 \ /
  Last update: 2018-04-17 19:00    [W:0.032 / U:0.336 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site