RS780 UVD cause hpet_readl() very slow

[Huacai Chen]

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