On Sat, Sep 8, 2018 at 10:54 PM Sergei Shtylyov
<sergei.shtylyov@xxxxxxxxxxxxxxxxxx> wrote:
> When trying to use CMT for clockevents on R-Car gen3 SoCs, I noticed
> that 'max_delta_ns' for the broadcast timer (CMT) was shown as 1000 in
> /proc/timer_list. It turned out that when calculating it, the driver did
> 1 << 32 (causing what I think was undefined behavior) resulting in a zero
> delta, later clamped to 1000 by cev_delta2ns(). The root cause turned out
> to be that the driver abused *unsigned long* for the CMT register values
> (which are 16/32-bit), so that the calculation of 'ch->max_match_value'
> in sh_cmt_setup_channel() used the wrong branch. Using more proper 'u32'
> instead fixed 'max_delta_ns' and even fixed the switching an active
> clocksource to CMT (which caused the system to turn non-interactive
> before).
>
> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
>
> ---
> This patch is against the 'tip.git' repo's 'timers/core' branch.
> The CMT driver wasn't ever used on SH64; on R-Car gen3 (ARM64) I'm only
> enabling building of this driver now, so not sure how urgent is this...
>
> Changes in version 3:
> - made the 'overflow_bit' and 'clear_bits' members of 'struct sh_cmt_info'
> 'u32';
> - made the 2nd parameter of sh_cmt_write_cmstr() 'u32';
> - made the result, the 2nd parameter, and 'o{1|2}' local variables of
> sh_cmt_get_counter() 'u32';
> - made the 'has_wrapped' local variables 'u32' in sh_cmt_clocksource_read()
> and sh_cmt_clock_event_program_verify();
> - fixed a typo in the patch description.
Thanks for the update!
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
