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

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Date:	Mon, 2 Feb 2015 08:53:37 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Mark yao <mark.yao@...k-chips.com>
Cc:	Daniel Kurtz <djkurtz@...omium.org>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel@...ll.ch>,
	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 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
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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