On Thu, Aug 21, 2014 at 01:29:03PM +0200, Takashi Iwai wrote:
> I did a quick hack and it seems working on my box.
> The patch is below.
Thanks!!
Further comments below.
I will be testing this ASAP.
> +static bool use_ktime = true;
> +module_param(use_ktime, bool, 0400);
Towards final commit, should probably add param docs on what may be switched here and why.
> +
> /*
> * gameport_mutex protects entire gameport subsystem and is taken
> * every time gameport port or driver registrered or unregistered.
> @@ -76,6 +80,36 @@ static unsigned int get_time_pit(void)
>
> static int gameport_measure_speed(struct gameport *gameport)
> {
> + unsigned int i, t, tx;
> + u64 t1, t2;
> + unsigned long flags;
> +
> + if (gameport_open(gameport, NULL, GAMEPORT_MODE_RAW))
> + return 0;
> +
> + tx = ~0;
> +
> + for (i = 0; i < 50; i++) {
> + local_irq_save(flags);
> + t1 = ktime_get_ns();
> + for (t = 0; t < 50; t++)
> + gameport_read(gameport);
> + t2 = ktime_get_ns();
> + local_irq_restore(flags);
> + udelay(i * 10);
> + if (t2 - t1 < tx)
> + tx = t2 - t1;
This impl is not doing the more complex t3, t2, t1 calculation
that the PIT impl is doing (likely for the uncommented purpose
of eliminating timer I/O delay from timing consideration).
Do/don't ktime/TSC impls better need such an I/O timing correction,
or are they so fast relative to gameport I/O delays
that it does not matter? (probably the case for TSC at least).
Oh, and any reason that such a speed calculation remains painfully duplicated
in both source files? That's possibly done for layering reasons,
but I'd have to analyze it further.
> +static inline u64 get_time(void)
> +{
> + if (use_ktime) {
> + return ktime_get_ns();
> + } else {
> + unsigned int x;
> + GET_TIME(x);
> + return x;
> + }
> +}
It might be useful to have a first commit to introduce these helpers,
and a second commit to then add ktime support (to keep review code size
down).
Thanks,
Andreas Mohr
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