linux-kernel - Re: [PATCH 1/2] drm: hdlcd: Skip PM callbacks if unbound

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Message-ID: <20160506162613.GL28464@e106497-lin.cambridge.arm.com>
Date:	Fri, 6 May 2016 17:26:13 +0100
From:	liviu.dudau@....com
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Robin Murphy <robin.murphy@....com>, airlied@...ux.ie,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] drm: hdlcd: Skip PM callbacks if unbound

On Fri, May 06, 2016 at 04:54:17PM +0200, Thierry Reding wrote:
> On Thu, May 05, 2016 at 05:13:37PM +0100, Robin Murphy wrote:
> > Until an encoder component is available to trigger the HDLCD's component
> > master bind callback, the drm_device we keep in drvdata isn't allocated.
> > Since it is quite possible to, say, hibernate the system without having
> > loaded the encoder driver, the PM callbacks need to check for a valid
> > drm_device before trying to take the lock and suspend/resume the crtcs,
> > otherwise this happens:
> > 
> > [   51.779092] Unable to handle kernel NULL pointer dereference at virtual address 00000200
> > [   51.787143] pgd = ffff800974462000
> > [   51.790514] [00000200] *pgd=0000000000000000
> > [   51.794768] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> > [   51.800291] Modules linked in:
> > [   51.803325] CPU: 4 PID: 2098 Comm: systemd-sleep Not tainted 4.6.0-rc6+ #4
> > [   51.810140] Hardware name: ARM Juno development board (r1) (DT)
> > [   51.816008] task: ffff800974430000 ti: ffff80097380c000 task.ti: ffff80097380c000
> > [   51.823433] PC is at mutex_lock+0x14/0x60
> > [   51.827411] LR is at drm_modeset_lock_all+0x3c/0xe0
> > [   51.832246] pc : [<ffff0000087d55c4>] lr : [<ffff0000084839fc>] pstate: 40000145
> > [   51.839577] sp : ffff80097380faf0
> > [   51.842859] x29: ffff80097380faf0 x28: 0000000000000000
> > [   51.848132] x27: 0000000000000002 x26: ffff000008e01000
> > [   51.853405] x25: ffff0000084cc000 x24: ffff000008dcb408
> > [   51.858678] x23: ffff000008e7c000 x22: ffff8009760e8870
> > [   51.863962] x21: 0000000000000200 x20: 0000000000000000
> > [   51.869244] x19: 0000000000000200 x18: ffff800079357dd0
> > [   51.874527] x17: 0000ffff8a00ab88 x16: 0000000000000018
> > [   51.879809] x15: 0000000000000018 x14: 0000000000000000
> > [   51.885091] x13: 0000000000000002 x12: 0000000000000000
> > [   51.890374] x11: ffff0000087ff904 x10: 0000000000000840
> > [   51.895656] x9 : 0000000000000000 x8 : ffff800973821680
> > [   51.900938] x7 : 0000000000000000 x6 : 000000000000003f
> > [   51.906220] x5 : 0000000000000040 x4 : 0000000000000000
> > [   51.911502] x3 : 0000000000000004 x2 : 0000000000000000
> > [   51.916784] x1 : 0000000000000001 x0 : 0000000000000200
> > ...
> > [   52.339406] [<ffff0000087d55c4>] mutex_lock+0x14/0x60
> > [   52.344425] [<ffff0000084839fc>] drm_modeset_lock_all+0x3c/0xe0
> > [   52.350305] [<ffff00000848a034>] hdlcd_pm_suspend+0x2c/0x90
> > [   52.355842] [<ffff0000084c0d14>] platform_pm_suspend+0x24/0x58
> > [   52.361638] [<ffff0000084cc190>] dpm_run_callback.isra.4+0x20/0x68
> > [   52.367778] [<ffff0000084ccad4>] __device_suspend+0xe4/0x238
> > [   52.373400] [<ffff0000084cdcac>] dpm_suspend+0x10c/0x240
> > [   52.378679] [<ffff0000084ce0b8>] dpm_suspend_start+0x70/0x80
> > [   52.384302] [<ffff0000080f80e4>] suspend_devices_and_enter+0x9c/0x480
> > [   52.390699] [<ffff0000080f8698>] pm_suspend+0x1d0/0x240
> > [   52.395890] [<ffff0000080f7280>] state_store+0x80/0x100
> > [   52.401084] [<ffff0000083503f4>] kobj_attr_store+0x14/0x28
> > [   52.406535] [<ffff000008238580>] sysfs_kf_write+0x48/0x58
> > [   52.411899] [<ffff00000823798c>] kernfs_fop_write+0xbc/0x188
> > [   52.417521] [<ffff0000081c71f4>] __vfs_write+0x1c/0xe0
> > [   52.422626] [<ffff0000081c8144>] vfs_write+0x8c/0x1a8
> > [   52.427644] [<ffff0000081c953c>] SyS_write+0x44/0xa0
> > [   52.432578] [<ffff000008084ecc>] __sys_trace_return+0x0/0x4
> > [   52.438114] Code: 910003fd f9000bf3 aa0003f3 f9800011 (885ffc01)
> > [   52.444229] ---[ end trace 34b87a5fb9453f65 ]---
> > 
> > Acked-by: Liviu Dudau <Liviu.Dudau@....com>
> > Signed-off-by: Robin Murphy <robin.murphy@....com>
> > ---
> >  drivers/gpu/drm/arm/hdlcd_drv.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/arm/hdlcd_drv.c b/drivers/gpu/drm/arm/hdlcd_drv.c
> > index 734899c4e4bb..86a5eea4cf53 100644
> > --- a/drivers/gpu/drm/arm/hdlcd_drv.c
> > +++ b/drivers/gpu/drm/arm/hdlcd_drv.c
> > @@ -498,7 +498,7 @@ static int __maybe_unused hdlcd_pm_suspend(struct device *dev)
> >  	struct drm_device *drm = dev_get_drvdata(dev);
> >  	struct drm_crtc *crtc;
> >  
> > -	if (pm_runtime_suspended(dev))
> > +	if (pm_runtime_suspended(dev) || !drm)
> >  		return 0;
> >  
> >  	drm_modeset_lock_all(drm);
> > @@ -513,7 +513,7 @@ static int __maybe_unused hdlcd_pm_resume(struct device *dev)
> >  	struct drm_device *drm = dev_get_drvdata(dev);
> >  	struct drm_crtc *crtc;
> >  
> > -	if (!pm_runtime_suspended(dev))
> > +	if (!pm_runtime_suspended(dev) || !drm)
> >  		return 0;
> 
> Perhaps rather than this workaround you should only enable runtime PM on
> this after the master has been bound?

Yes, that is probably a better solution, even if the patch is going to be much bigger.

Best regards,
Liviu

> 
> Thierry


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