linux-kernel - Re: [PATCH 1/1] drm: fsl-dcu: Use flat cache

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Date:	Fri, 25 Mar 2016 09:24:28 -0700
From:	Stefan Agner <stefan@...er.ch>
To:	Alexander Stein <alexander.stein@...tec-electronic.com>
Cc:	Alison Wang <alison.wang@...escale.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] drm: fsl-dcu: Use flat cache

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@...tec-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.

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

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.

--
Stefan

>  
>  	.volatile_reg = fsl_dcu_drm_is_volatile_reg,
>  };