RS780 UVD cause hpet_readl() very slow

[Huacai Chen]

Yes, USB device can fixes the issue (only attaching a device has no
effect, attching and do data transferring can fix).

Huacai

On Fri, Jun 17, 2016 at 5:31 PM, Koenig, Christian
<Christian.Koenig at amd.com> wrote:
> Hi Huacai,
>
> Adding our internal list on CC as well, maybe somebody else has an idea.
>
> I unfortunately don't understand at all how playing something with UVD could
> delay a simple register read by about 1ms.
>
> And do I get that right that attaching something to the USB controller on
> the south bridge fixes the issue?
>
> Additional to that the RS780 is already rather old and we don't have any
> hardware for testing that generation any more.
>
> Sorry no idea of hand,
> Christina.
>
> Am 17.06.2016 10:52 schrieb Huacai Chen <chenhuacai at gmail.com>:
>
> Hi, Christian
>
> We found that if we use RS780 UVD decoding, hpet_readl() will need as
> long as 1ms.
> But, if attach a U-disk on south bridge (SB700) and read some data
> from it, hpet_readl() has no problem.
> Could you please give me some suggestions or fix it?
>
> How to reproduce:
> 1, apply the patch on top of kernel (4.2+) and boot with this kernel
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 307a498..a0c8634 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -452,10 +452,12 @@ EXPORT_SYMBOL_GPL(setup_APIC_eilvt);
>  /*
>   * Program the next event, relative to now
>   */
> +void check_hpet(void);
>  static int lapic_next_event(unsigned long delta,
>                             struct clock_event_device *evt)
>  {
>         apic_write(APIC_TMICT, delta);
> +       check_hpet();
>         return 0;
>  }
>
> diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> index 3acbff4..19329e8 100644
> --- a/arch/x86/kernel/hpet.c
> +++ b/arch/x86/kernel/hpet.c
> @@ -367,6 +367,15 @@ static void hpet_set_mode(enum clock_event_mode mode,
>         }
>  }
>
> +void check_hpet(void)
> +{
> +       u32 cnt1,cnt2;
> +
> +       cnt1 = hpet_readl(HPET_COUNTER);
> +       cnt2 = hpet_readl(HPET_COUNTER);
> +       if(cnt2-cnt1>1000) printk("So big! (%u)\n",cnt2-cnt1);
> +}
> +
>  static int hpet_next_event(unsigned long delta,
>                            struct clock_event_device *evt, int timer)
>  {
>
> 2, ensure that no USB device attached on SB700 (except keyboard and mouse)
> 3, download this file:
> http://mirror.lemote.com/fedora-users/ipfootball/video_bench/1920x1080_25fps_h264_ac3.mkv
> 4, ffmpeg -hwaccel vdpau -i 1920x1080_25fps_h264_acc.mkv  -f rawvideo
> -an -y /dev/null
> 5, dmesg will complain "So big..."
>
> Huacai