Clemens Ladisch wrote: [Thu Sep 22 2005, 11:08:41AM EDT]
> On 32-bit architectures, the multiplication in the argument for
> hpet_time_div() often overflows. In the typical case of a 14.32 MHz
> timer, this happens when the desired frequency exceeds 61 Hz.
>
> To avoid this multiplication, we can precompute and store the hardware
> timer frequency, instead of the period, in the device structure, which
> leaves us with a simple division when computing the number of timer
> ticks.
>
> As a side effect, this also removes a theoretical bug where the timer
> interpolator's frequency would be computed as a 32-bit value even if
> the HPET frequency is greater than 2^32 Hz (the HPET spec allows up to
> 10 GHz).
>
> Signed-off-by: Clemens Ladisch <[email protected]>
>
> --- linux-2.6.13.orig/drivers/char/hpet.c 2005-09-22 11:10:01.000000000 +0200
> +++ linux-2.6.13/drivers/char/hpet.c 2005-09-22 12:08:48.000000000 +0200
> @@ -78,7 +78,7 @@ struct hpets {
> struct hpet __iomem *hp_hpet;
> unsigned long hp_hpet_phys;
> struct time_interpolator *hp_interpolator;
> - unsigned long hp_period;
> + unsigned long long hp_tick_freq;
> unsigned long hp_delta;
> unsigned int hp_ntimer;
> unsigned int hp_which;
> @@ -427,12 +427,14 @@ static int hpet_ioctl_ieon(struct hpet_d
> return 0;
> }
>
> -static inline unsigned long hpet_time_div(unsigned long dis)
> +/* converts Hz to number of timer ticks */
> +static inline unsigned long hpet_time_div(struct hpets *hpets,
> + unsigned long dis)
> {
> - unsigned long long m = 1000000000000000ULL;
> + unsigned long long m;
>
> + m = hpets->hp_tick_freq + (dis >> 1);
> do_div(m, dis);
> -
> return (unsigned long)m;
> }
>
> @@ -480,7 +482,7 @@ hpet_ioctl_common(struct hpet_dev *devp,
> {
> struct hpet_info info;
>
> - info.hi_ireqfreq = hpet_time_div(hpetp->hp_period *
> + info.hi_ireqfreq = hpet_time_div(hpetp,
> devp->hd_ireqfreq);
> info.hi_flags =
> readq(&timer->hpet_config) & Tn_PER_INT_CAP_MASK;
> @@ -524,7 +526,7 @@ hpet_ioctl_common(struct hpet_dev *devp,
> break;
> }
>
> - devp->hd_ireqfreq = hpet_time_div(hpetp->hp_period * arg);
> + devp->hd_ireqfreq = hpet_time_div(hpetp, arg);
> }
>
> return err;
> @@ -713,7 +715,7 @@ static void hpet_register_interpolator(s
> ti->source = TIME_SOURCE_MMIO64;
> ti->shift = 10;
> ti->addr = &hpetp->hp_hpet->hpet_mc;
> - ti->frequency = hpet_time_div(hpets->hp_period);
> + ti->frequency = hpetp->hp_tick_freq;
> ti->drift = ti->frequency * HPET_DRIFT / 1000000;
> ti->mask = -1;
>
> @@ -750,7 +752,7 @@ static unsigned long hpet_calibrate(stru
> t = read_counter(&timer->hpet_compare);
>
> i = 0;
> - count = hpet_time_div(hpetp->hp_period * TICK_CALIBRATE);
> + count = hpet_time_div(hpetp, TICK_CALIBRATE);
>
> local_irq_save(flags);
>
> @@ -775,7 +777,8 @@ int hpet_alloc(struct hpet_data *hdp)
> size_t siz;
> struct hpet __iomem *hpet;
> static struct hpets *last = (struct hpets *)0;
> - unsigned long ns;
> + unsigned long ns, period;
> + unsigned long long temp;
>
> /*
> * hpet_alloc can be called by platform dependent code.
> @@ -825,8 +828,12 @@ int hpet_alloc(struct hpet_data *hdp)
>
> last = hpetp;
>
> - hpetp->hp_period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
> - HPET_COUNTER_CLK_PERIOD_SHIFT;
> + period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
> + HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */
> + temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */
> + temp += period >> 1; /* round */
> + do_div(temp, period);
> + hpetp->hp_tick_freq = temp; /* ticks per second */
>
> printk(KERN_INFO "hpet%d: at MMIO 0x%lx, IRQ%s",
> hpetp->hp_which, hdp->hd_phys_address,
> @@ -835,8 +842,7 @@ int hpet_alloc(struct hpet_data *hdp)
> printk("%s %d", i > 0 ? "," : "", hdp->hd_irq[i]);
> printk("\n");
>
> - ns = hpetp->hp_period; /* femptoseconds, 10^-15 */
> - ns /= 1000000; /* convert to nanoseconds, 10^-9 */
> + ns = period / 1000000; /* convert to nanoseconds, 10^-9 */
> printk(KERN_INFO "hpet%d: %ldns tick, %d %d-bit timers\n",
> hpetp->hp_which, ns, hpetp->hp_ntimer,
> cap & HPET_COUNTER_SIZE_MASK ? 64 : 32);
> -
Sorry for the delay. Looks like my 32 bit code isn't correct for >61 Hz
Never had a 32 bit arch with HPET for testing. This patch looks fine.
thanks,
bob
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |