linux-kernel - Re: [PATCH] drm/rockchip: vop: power off until vop standby take effect

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Date:	Wed, 04 Feb 2015 11:38:14 +0800
From:	Mark yao <mark.yao@...k-chips.com>
To:	Daniel Kurtz <djkurtz@...omium.org>,
	David Airlie <airlied@...ux.ie>,
	Rob Clark <robdclark@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH] drm/rockchip: vop: power off until vop standby take effect

On 2015年02月02日 15:53, Daniel Vetter wrote:
> On Mon, Feb 02, 2015 at 10:30:09AM +0800, Mark yao wrote:
>> On 2015年02月02日 10:07, Daniel Kurtz wrote:
>>> Hi Mark, Heiko,
>>>
>>> On Sat, Jan 31, 2015 at 4:41 PM, Mark Yao <mark.yao@...k-chips.com> wrote:
>>>> Vop standby will take effect end of current frame,
>>>> if dsp_hold_valid_irq happen, it means vop standby complete.
>>>>
>>>> we must wait standby complete when we want to disable aclk,
>>>> if not, memory bus maybe dead.
>>>>
>>>> Signed-off-by: Mark Yao <mark.yao@...k-chips.com>
>>>> ---
>>>>   drivers/gpu/drm/rockchip/rockchip_drm_vop.c |   76 ++++++++++++++++++++++-----
>>>>   1 file changed, 63 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>>>> index fb25836..47ea61f 100644
>>>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>>>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
>>>> @@ -89,6 +89,7 @@ struct vop {
>>>>          /* mutex vsync_ work */
>>>>          struct mutex vsync_mutex;
>>>>          bool vsync_work_pending;
>>>> +       struct completion dsp_hold_completion;
>>>>
>>>>          const struct vop_data *data;
>>>>
>>>> @@ -382,6 +383,34 @@ static bool is_alpha_support(uint32_t format)
>>>>          }
>>>>   }
>>>>
>>>> +static void vop_dsp_hold_valid_irq_enable(struct vop *vop)
>>>> +{
>>>> +       unsigned long flags;
>>>> +
>>>> +       BUG_ON(!vop->is_enabled);
>>> Re: Heiko "use a WARN_ON":
>>>
>>> If the VOP clock is off, then the system will just hang when trying to
>>> write the VOP register so in this case, BUG_ON gives a more reliable
>>> crash dump than the hang.
>>    In this way, you are right, if vop clocks is disabled, write vop register
>> will hang system, and the WARN_ON
> if (WARN_ON(cond))
> 	return;
>
> is what we commonly use in i915. Because it's really not any good to use
> BUG_ON in drm drivers, at least if you expect anyone to use fbcon on top
> of it (i.e. anything even remotely resembling a normal distro): Then the
> intial modeset is all done under console_lock, which means that _none_ of
> your BUG_ON will ever get out over serial console.
>
> The problem is fbcon locking, but no fool yet signed up to fix it (it's
> horrible, I looked ...).
> -Daniel
I know this problem, if fbcon locking, and BUG_ON, we can't get any log 
from serial console, Trouble
me many times. So know, if no drm log output, the first thing I do is 
remove the fbcon lock, and then
we can see the crash dump.

But here, I expect to use BUG_ON, because if BUG happen, vop register 
will hang system, and WARN_ON
may be have no chance to output.

Mark

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