Re: Re: [PATCHv3 0/8] devfreq: Add generic exynos memory-bus frequency driver

[MyungJoo Ham <myungjoo.ham@samsung.com>]

> Hello Chanwoo!
> 
> Chanwoo Choi wrote:
> > As you thought, when maintaining lower clock of memory bus frequency,
> > some issue related to multimedia feature will happen.
> > 
> > Separately, We have to check the miminum lower clock for working of multimedia feature.
> > and then multimedia or other IP have to request it to DVFS driver (memory busfreq driver).
> > But, latest mainline kernel currently has not some way to inform minimum clock to DVFS driver.
> > 
> > So, If you check the miminum clock for hdmi, I'll use this clock as minumu frequency of dvfs table.
> > 
> > Thanks,
> > Chanwoo Choi
> > 
> 
> First I have to apologize. I didn't check carefully. Actually it's not
> the HDMI subsystem which seems to hang during my test, but the G2D
> subsystem.
> 
> Here's a snippet of the kernel log with drm.debug=0xff:
> [ 1157.911264] [drm:drm_framebuffer_reference] ee144e00: FB ID: 27 (2)
> [ 1157.911271] [drm:drm_framebuffer_unreference] ee37fb80: FB ID: 25 (2)
> [ 1157.911277] [drm:drm_framebuffer_unreference] ee144e00: FB ID: 27 (3)
> [ 1157.911315] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> EXYNOS_G2D_GET_VER
> [ 1158.434439] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> EXYNOS_G2D_SET_CMDLIST
> [ 1158.434536] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1, EXYNOS_G2D_EXEC
> [ 1158.437484] [drm:drm_vm_close_locked] 0xaf840000,0x00140000
> [ 1158.437507] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> DRM_IOCTL_GEM_CLOSE
> [ 1158.437524] [drm:exynos_drm_gem_destroy] handle count = 0
> [ 1158.437532] [drm:lowlevel_buffer_deallocate] dma_addr(0x20500000),
> size(0x140000)
> [ 1158.437810] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> EXYNOS_GEM_CREATE
> [ 1158.437819] [drm:exynos_drm_init_buf] desired size = 0x256000
> [ 1158.437851] [drm:exynos_drm_gem_init] created file object = 0xe97c8d00
> [ 1158.445506] [drm:lowlevel_buffer_allocate] dma_addr(0x21400000),
> size(0x256000)
> [ 1158.445535] [drm:exynos_drm_gem_handle_create] gem handle = 0x1
> [ 1158.445556] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> DRM_IOCTL_MODE_MAP_DUMB
> [ 1158.445570] [drm:exynos_drm_gem_dumb_map_offset] offset = 0x101c2000
> [ 1158.445600] [drm:drm_vm_open_locked] 0xaec15000,0x00256000
> [ 1158.445608] [drm:update_vm_cache_attr] flags = 0x0
> [ 1158.457696] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1,
> EXYNOS_G2D_SET_CMDLIST
> [ 1158.457745] [drm:drm_ioctl] pid=2569, dev=0xe200, auth=1, EXYNOS_G2D_EXEC
> 
> 
> So G2D_EXEC seems to work once, but the second time it hangs forever. I
> even fail at attaching gdb to the application then (gdb then also hangs
> in D state).
> 
> If I just use the 'vsynced page flipping' test, then everything works:
> ./modetest -M exynos -s 16@13:1280x720 -v
> setting mode 1280x720-60Hz@XR24 on connectors 16, crtc 13
> freq: 61.08Hz
> freq: 60.00Hz
> freq: 60.00Hz
> <etc.>
> 
> I'm going to do some tests with the G2D in the next time, checking how
> much I can lower MIF/INT clocks before the engine becomes unstable.
> 
> With best wishes,
> Tobias
> 
> 

Unless you are willing to wait for 2 minutes after the kernal hangs,
you may want to adjust "DEFAULT_HUNG_TASK_TIMEOUT" to shorter value
(120 --> 5 for 5 seconds). It seems that you've cut it off in the middle
of that "120 sec" wait.

If it's in D state (in kernel), gdb won't work as you are experiencing.
Sorry for not testing with HDMI; my Exynos devices do not have HDMI. :)

To Chanwoo, wouldn't it be ok to have the corresponding devfreq driver
to set minimum higher IFF HDMI is enabled? (either by build time or
run time) I guess Exynos HDMI driver should express PM-QoS requests later.
(Or let Exynos HDMI driver not hung even if its memory transactions are
not fast enough)

Cheers,
MyungJoo