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

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Message-ID: <20180308224717.a6ieadihwh7u5rbu@core.my.home>
Date:   Thu, 8 Mar 2018 23:47:17 +0100
From:   Ondřej Jirman <megi@....cz>
To:     Jernej Skrabec <jernej.skrabec@...l.net>
Cc:     maxime.ripard@...e-electrons.com, wens@...e.org, airlied@...ux.ie,
        robh+dt@...nel.org, mark.rutland@....com, mturquette@...libre.com,
        sboyd@...nel.org, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [linux-sunxi] [PATCH v3 06/16] drm/sun4i: Release exclusive
 clock lock when disabling TCON

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@...l.net>
> ---
>  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:

$ 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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