Hi Sergei,
On Tue, Sep 4, 2018 at 8:32 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 worng 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 2:
> - completely redid the patch, fixing abuse of *unsigned long* for the CMT
> register values.
Thanks for the update!
> --- tip.orig/drivers/clocksource/sh_cmt.c
> +++ tip/drivers/clocksource/sh_cmt.c
> @@ -82,14 +82,13 @@ struct sh_cmt_info {
> unsigned long clear_bits;
"clear_bits" should be u32, as it corresponds to a register value.
>
> /* callbacks for CMSTR and CMCSR access */
> - unsigned long (*read_control)(void __iomem *base, unsigned long offs);
> + u32 (*read_control)(void __iomem *base, unsigned long offs);
> void (*write_control)(void __iomem *base, unsigned long offs,
> - unsigned long value);
> + u32 value);
>
> /* callbacks for CMCNT and CMCOR access */
> - unsigned long (*read_count)(void __iomem *base, unsigned long offs);
> - void (*write_count)(void __iomem *base, unsigned long offs,
> - unsigned long value);
> + u32 (*read_count)(void __iomem *base, unsigned long offs);
> + void (*write_count)(void __iomem *base, unsigned long offs, u32 value);
> };
>
> struct sh_cmt_channel {
> @@ -103,9 +102,9 @@ struct sh_cmt_channel {
>
> unsigned int timer_bit;
> unsigned long flags;
While no register value, "flags" can be unsigned int, too.
> - unsigned long match_value;
> - unsigned long next_match_value;
> - unsigned long max_match_value;
> + u32 match_value;
> + u32 next_match_value;
> + u32 max_match_value;
> raw_spinlock_t lock;
> struct clock_event_device ced;
> struct clocksource cs;
> @@ -290,7 +284,7 @@ static inline void sh_cmt_write_cmcor(st
> static unsigned long sh_cmt_get_counter(struct sh_cmt_channel *ch,
Return type should be "u32".
> int *has_wrapped)
While not "unsigned long", "has_wrapped" is used to store a register value,
so I think it should be changed to "u32 *".
> {
> - unsigned long v1, v2, v3;
> + u32 v1, v2, v3;
> int o1, o2;
While not "unsigned long", "o1" and "o2" contain register values, so I think
they should be "u32".
> o1 = sh_cmt_read_cmcsr(ch) & ch->cmt->info->overflow_bit;
"overflow_bit" should become "u32", too.
> @@ -619,9 +614,10 @@ static struct sh_cmt_channel *cs_to_sh_c
> static u64 sh_cmt_clocksource_read(struct clocksource *cs)
> {
> struct sh_cmt_channel *ch = cs_to_sh_cmt(cs);
> - unsigned long flags, raw;
> + unsigned long flags;
> unsigned long value;
> int has_wrapped;
> + u32 raw;
>
> raw_spin_lock_irqsave(&ch->lock, flags);
> value = ch->total_cycles;
"value" and "total_cycles" should be "u64". But that's a separate bug fix.
Not in the context, so I cannot comment to it, but "sh_cmt_info.width" should
be "unsigned int", too.
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
