From: Alexander Stein <alexander.stein@systec-electronic.com>
To: Stefan Agner <stefan@agner.ch>
Cc: Alison Wang <alison.wang@freescale.com>, David Airlie <airlied@linux.ie>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/1] drm: fsl-dcu: Use flat cache
Date: Tue, 29 Mar 2016 08:56:12 +0200
Message-ID: <16406347.uLoyTglLnv@ws-stein>
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On Friday 25 March 2016 09:24:28, Stefan Agner wrote:
> Hi Alexander,
> 
> On 2016-03-24 06:33, Alexander Stein wrote:
> > Using REGCACHE_RBTREE for MMIO regmap is not valid as spinlock's will be
> > used during cache allocation.
> > 
> > This fixes the following bug:
> > BUG: sleeping function called from invalid context at mm/slab.h:388
> > in_atomic(): 1, irqs_disabled(): 128, pid: 192, name: udevd
> > [...]
> > 
> > Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
> > ---
> > Please refer also to the discussion at
> > https://lists.freedesktop.org/archives/dri-devel/2016-January/098696.html
> > 
> >  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > index e8d9337..ea65140 100644
> > --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> > @@ -40,7 +40,7 @@ static const struct regmap_config fsl_dcu_regmap_config
> > = {> 
> >  	.reg_bits = 32,
> >  	.reg_stride = 4,
> >  	.val_bits = 32,
> > 
> > -	.cache_type = REGCACHE_RBTREE,
> > +	.cache_type = REGCACHE_FLAT,
> 
> To use flat regcache you also need to set the max_register.

Ah, thanks for that hint, I was not aware of that. I wondered why my kernel 
crashed using flat cache. Seems cache allocation is too small when 
max_register=0.
Just sent a patch enforcing setting max_register.

> I already have such a patch, see:
> https://lists.freedesktop.org/archives/dri-devel/2016-January/099121.html

Thanks, meanwhile this will do for me. I think.

> However, the current suspend/resume implementation (which uses the
> regcache) is anyway flawed. I currently prepare a patchset to remove the
> regmap cache entirely and use Thierry's new generic suspend/resume
> functions.

Feel free to cc me.
Best regards,
Alexander