linux-kernel - Re: [PATCH 2/2] drm/fsl-dcu: use flat regmap cache

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Date:	Tue, 02 Feb 2016 16:39:01 -0800
From:	Stefan Agner <stefan@...er.ch>
To:	dri-devel@...ts.freedesktop.org
Cc:	airlied@...ux.ie, daniel.vetter@...ll.ch,
	jianwei.wang.chn@...il.com, alison.wang@...escale.com,
	meng.yi@....com, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 2/2] drm/fsl-dcu: use flat regmap cache

On 2016-01-20 18:50, Stefan Agner wrote:
> Using flat regmap cache instead of RB-tree to avoid the following
> lockdep warning on driver load:
> [    0.697285] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755
> lockdep_trace_alloc+0x15c/0x160()
> [    0.697449] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> 
> The RB-tree regmap cache needs to allocate new space on first
> writes. However, allocations in an atomic context (e.g. when a
> spinlock is held) are not allowed. The function regmap_write
> calls map->lock, which acquires a spinlock in the fast_io case.
> Since the FSL DCU driver uses MMIO, the regmap bus of type
> regmap_mmio is being used which has fast_io set to true.
> 
> The MMIO space of the DCU driver is reasonable condense, hence
> using the much faster flat regmap cache is anyway the better
> choice.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> Cc: Mark Brown <broonie@...nel.org>
> ---
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 20 ++++++++++++--------
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h |  6 ++++--
>  2 files changed, 16 insertions(+), 10 deletions(-)
> 
> 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 e01c813..971c520 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> @@ -36,11 +36,11 @@ static bool fsl_dcu_drm_is_volatile_reg(struct
> device *dev, unsigned int reg)
>  	return false;
>  }
>  
> -static const struct regmap_config fsl_dcu_regmap_config = {
> +static struct regmap_config fsl_dcu_regmap_config = {
>  	.reg_bits = 32,
>  	.reg_stride = 4,
>  	.val_bits = 32,
> -	.cache_type = REGCACHE_RBTREE,
> +	.cache_type = REGCACHE_FLAT,
>  
>  	.volatile_reg = fsl_dcu_drm_is_volatile_reg,
>  };
> @@ -260,12 +260,14 @@ static const struct fsl_dcu_soc_data
> fsl_dcu_ls1021a_data = {
>  	.name = "ls1021a",
>  	.total_layer = 16,
>  	.max_layer = 4,
> +	.max_register = LS1021A_DCU_MAX_REGISTER,
>  };
>  
>  static const struct fsl_dcu_soc_data fsl_dcu_vf610_data = {
>  	.name = "vf610",
>  	.total_layer = 64,
>  	.max_layer = 6,
> +	.max_register = VF610_DCU_MAX_REGISTER,
>  };
>  
>  static const struct of_device_id fsl_dcu_of_match[] = {
> @@ -331,6 +333,14 @@ static int fsl_dcu_drm_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  
> +	id = of_match_node(fsl_dcu_of_match, pdev->dev.of_node);
> +	if (!id)
> +		return -ENODEV;
> +
> +	drm = drm_dev_alloc(driver, dev);
> +	fsl_dev->soc = id->data;
> +
> +	fsl_dcu_regmap_config.max_register = fsl_dev->soc->max_register;
>  	fsl_dev->regmap = devm_regmap_init_mmio(dev, base,
>  			&fsl_dcu_regmap_config);
>  	if (IS_ERR(fsl_dev->regmap)) {
> @@ -338,12 +348,6 @@ static int fsl_dcu_drm_probe(struct platform_device *pdev)
>  		return PTR_ERR(fsl_dev->regmap);
>  	}
>  
> -	id = of_match_node(fsl_dcu_of_match, pdev->dev.of_node);
> -	if (!id)
> -		return -ENODEV;
> -	fsl_dev->soc = id->data;
> -
> -	drm = drm_dev_alloc(driver, dev);
>  	if (!drm)
>  		return -ENOMEM;


The drm_dev_alloc call should be close to its error handling, and moving
is anyway not necessary...

Will fix that in v2

--
Stefan

>  
> diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> index 2a724f3..7c296a0 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> @@ -114,8 +114,6 @@
>  #define DCU_UPDATE_MODE_MODE		BIT(31)
>  #define DCU_UPDATE_MODE_READREG		BIT(30)
>  
> -#define DCU_DCFB_MAX			0x300
> -
>  #define DCU_CTRLDESCLN(layer, reg)	(0x200 + (reg - 1) * 4 + (layer) * 0x40)
>  
>  #define DCU_LAYER_HEIGHT(x)		((x) << 16)
> @@ -155,6 +153,9 @@
>  #define DCU_LAYER_POST_SKIP(x)		((x) << 16)
>  #define DCU_LAYER_PRE_SKIP(x)		(x)
>  
> +#define VF610_DCU_MAX_REGISTER		0x11fc
> +#define LS1021A_DCU_MAX_REGISTER	0x5fc
> +
>  #define FSL_DCU_RGB565			4
>  #define FSL_DCU_RGB888			5
>  #define FSL_DCU_ARGB8888		6
> @@ -175,6 +176,7 @@ struct fsl_dcu_soc_data {
>  	unsigned int total_layer;
>  	/*max layer number DCU supported*/
>  	unsigned int max_layer;
> +	unsigned int max_register;
>  };
>  
>  struct fsl_dcu_drm_device {