Re: [PATCH v3 06/16] drm/sun4i: Release exclusive clock lock when disabling TCON

["'Ondřej Jirman' via linux-sunxi" <linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org>]

Hi,

I've debugged this further and it seems that the code has incorrect assumptions.
See docs for mode_set_nofb.

https://elixir.bootlin.com/linux/v4.16-rc4/source/include/drm/drm_modeset_helper_vtables.h#L209

I've added traces to a few functions that call clk_.*exclusive.*() functions,
and I see this after a few restarts of Xorg server:

[    0.783842] *** sun4i_tcon1_mode_set()
[    0.783886] *** sun4i_tcon_channel_set_status(..., 1, true)
[    6.881690] *** sun4i_tcon_channel_set_status(..., 1, false)
[    6.881758] *** sun4i_tcon_channel_set_status(..., 1, true)
[   52.335085] *** sun4i_tcon_channel_set_status(..., 1, false)
[   52.335343] *** sun4i_tcon_channel_set_status(..., 1, true)
[   68.921079] *** sun4i_tcon_channel_set_status(..., 1, false)
[   68.921337] *** sun4i_tcon_channel_set_status(..., 1, true)

mode_set_nofb is called just once, yet sun4i_tcon_channel_set_status(..., 1, false)
is called multiple times, which leads to unbalanced calls to clk_set_rate_exclusive
and clk_rate_exclusive_put.

I don't know how to fix this.

regards,
  o.

On Fri, Mar 09, 2018 at 01:13:14AM +0100, 'Ondřej Jirman' via linux-sunxi wrote:
> Hi Jernej,
> 
> On Thu, Mar 08, 2018 at 11:57:40PM +0100, Jernej Škrabec wrote:
> > Hi,
> > 
> > Dne četrtek, 08. marec 2018 ob 23:47:17 CET je Ondřej Jirman napisal(a):
> > > Hi,
> > > 
> > > On Thu, Mar 01, 2018 at 10:34:32PM +0100, Jernej Skrabec wrote:
> > > > Currently exclusive TCON clock lock is never released, which, for
> > > > example, prevents changing resolution on HDMI.
> > > > 
> > > > In order to fix that, release clock when disabling TCON. TCON is always
> > > > disabled first before new mode is set.
> > > > 
> > > > Signed-off-by: Jernej Skrabec <jernej.skrabec-gGgVlfcn5nU@public.gmane.org>
> > > > ---
> > > > 
> > > >  drivers/gpu/drm/sun4i/sun4i_tcon.c | 6 ++++--
> > > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > b/drivers/gpu/drm/sun4i/sun4i_tcon.c index 1d714c06ec9d..7f6c4125c89f
> > > > 100644
> > > > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > > > @@ -102,10 +102,12 @@ static void sun4i_tcon_channel_set_status(struct
> > > > sun4i_tcon *tcon, int channel,> 
> > > >  		return;
> > > >  	
> > > >  	}
> > > > 
> > > > -	if (enabled)
> > > > +	if (enabled) {
> > > > 
> > > >  		clk_prepare_enable(clk);
> > > > 
> > > > -	else
> > > > +	} else {
> > > > +		clk_rate_exclusive_put(clk);
> > > > 
> > > >  		clk_disable_unprepare(clk);
> > > > 
> > > > +	}
> > > > 
> > > >  }
> > > 
> > > At least in the linux-next/master I can't see clk_rate_exclusive_get call:
> > > 
> > 
> > It is in drm-misc/drm-misc-fixes:
> > https://cgit.freedesktop.org/drm/drm-misc/commit/?h=drm-misc-fixes&id=79d103a565d16b1893d990b2ee5e0fe71767759f
> > 
> > My patch is also applied in same branch, so there should be no issues while 
> > merging all those branches.
> > 
> > linux-next doesn't have either patches currently: https://git.kernel.org/pub/
> > scm/linux/kernel/git/next/linux-next.git/log/drivers/gpu/drm/sun4i
> > 
> > This is issue only if you manually apply one patch without the other.
> 
> I have (and had) both patches applied. There's perhaps some code path,
> where sun4i_tcon_channel_set_status(..., false) is called in unbalanced
> way with regards to clk_set_rate_exclusive().
> 
> The issue occurs when starting Xorg. But Xorg works fine.
> 
> regards,
>   o.
> 
> > Best regards,
> > Jernej
> > 
> > > $ git grep 'exclusive' linux-next/master -- drivers/gpu/drm/sun4i
> > > 
> > > linux-next/master:sun4i_hdmi.h:    * On sun5i the threshold is exclusive,
> > > i.e. does not include, linux-next/master:sun4i_tcon.c:          
> > > clk_rate_exclusive_put(clk); linux-next/master:sun4i_tcon.c:  
> > > clk_set_rate_exclusive(tcon->dclk, mode->crtc_clock * 1000);
> > > linux-next/master:sun4i_tcon.c:   clk_set_rate_exclusive(tcon->sclk1,
> > > mode->crtc_clock * 1000);
> > > 
> > > and the kernel complains too:
> > > 
> > > [  841.915161] ------------[ cut here ]------------
> > > [  841.915187] WARNING: CPU: 0 PID: 273 at
> > > /workspace/megous.com/orangepi-pc/linux-4.16/drivers/clk/clk.c:608
> > > clk_rate_exclusive_put+0x48/0x4c [  841.915194] CPU: 0 PID: 273 Comm: Xorg
> > > Not tainted 4.16.0-rc4-00268-gbac2ecf73ed0 #13 [  841.915196] Hardware
> > > name: Allwinner sun8i Family
> > > [  841.915217] [<c0228440>] (unwind_backtrace) from [<c0225b90>]
> > > (show_stack+0x10/0x14) [  841.915228] [<c0225b90>] (show_stack) from
> > > [<c0b094bc>] (dump_stack+0x88/0x9c) [  841.915237] [<c0b094bc>]
> > > (dump_stack) from [<c0240294>] (__warn+0xd4/0xf0) [  841.915244]
> > > [<c0240294>] (__warn) from [<c0240380>] (warn_slowpath_null+0x40/0x48) [ 
> > > 841.915250] [<c0240380>] (warn_slowpath_null) from [<c0619b6c>]
> > > (clk_rate_exclusive_put+0x48/0x4c) [  841.915261] [<c0619b6c>]
> > > (clk_rate_exclusive_put) from [<c0694624>]
> > > (sun4i_tcon_set_status+0x178/0x2f0) [  841.915269] [<c0694624>]
> > > (sun4i_tcon_set_status) from [<c06930c0>]
> > > (sun4i_crtc_atomic_disable+0x7c/0xe4) [  841.915279] [<c06930c0>]
> > > (sun4i_crtc_atomic_disable) from [<c06637fc>]
> > > (drm_atomic_helper_commit_modeset_disables+0x390/0x46c) [  841.915288]
> > > [<c06637fc>] (drm_atomic_helper_commit_modeset_disables) from [<c0664df4>]
> > > (drm_atomic_helper_commit_tail_rpm+0x18/0x64) [  841.915295] [<c0664df4>]
> > > (drm_atomic_helper_commit_tail_rpm) from [<c0664da8>]
> > > (commit_tail+0x40/0x6c) [  841.915302] [<c0664da8>] (commit_tail) from
> > > [<c06652b0>] (drm_atomic_helper_commit+0xbc/0x128) [  841.915311]
> > > [<c06652b0>] (drm_atomic_helper_commit) from [<c0668d40>]
> > > (restore_fbdev_mode_atomic+0x100/0x1fc) [  841.915319] [<c0668d40>]
> > > (restore_fbdev_mode_atomic) from [<c0668f1c>]
> > > (drm_fb_helper_dpms+0x50/0x130) [  841.915328] [<c0668f1c>]
> > > (drm_fb_helper_dpms) from [<c0669e9c>] (drm_fb_helper_blank+0x54/0x90) [ 
> > > 841.915337] [<c0669e9c>] (drm_fb_helper_blank) from [<c06088cc>]
> > > (fb_blank+0x54/0xa8) [  841.915343] [<c06088cc>] (fb_blank) from
> > > [<c0608c80>] (do_fb_ioctl+0x360/0x62c) [  841.915351] [<c0608c80>]
> > > (do_fb_ioctl) from [<c0362648>] (do_vfs_ioctl+0x9c/0x774) [  841.915358]
> > > [<c0362648>] (do_vfs_ioctl) from [<c0362d54>] (SyS_ioctl+0x34/0x58) [ 
> > > 841.915364] [<c0362d54>] (SyS_ioctl) from [<c0201120>]
> > > (ret_fast_syscall+0x0/0x4c) [  841.915368] Exception stack(0xe5fc5fa8 to
> > > 0xe5fc5ff0)
> > > [  841.915373] 5fa0:                   00674f10 00675460 0000000b 00004611
> > > 00000001 00000000 [  841.915379] 5fc0: 00674f10 00675460 00000001 00000036
> > > 00650474 00000000 006504a4 00675df8 [  841.915382] 5fe0: b61a502c be8acb2c
> > > b6192c38 b6b152ec
> > > [  841.915386] ---[ end trace fa81b956197707f8 ]---
> > > 
> > > It looks like clk_rate_exclusive_put inside sun4i_tcon_channel_set_status is
> > > called without first calling some function that would call
> > > clk_set_rate_exclusive, leading to unbalanced get/put calls.
> > > 
> > > regards,
> > >   o.
> > > 
> > > >  static void sun4i_tcon_lvds_set_status(struct sun4i_tcon *tcon,
> > > > 
> > > > --
> > > > 2.16.2
> > > > 
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