linux-kernel - Re: [RESEND 2/2] drm: fsl-dcu: enable PIXCLK on LS1021A

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Message-ID: <pkpza56m6a7oeuuq5374l27kgeyemhbsnmbswnuyurqzbqpek5@rxh3arxdw7ve>
Date: Sun, 22 Sep 2024 23:16:59 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Alexander Stein <alexander.stein@...tq-group.com>
Cc: Stefan Agner <stefan@...er.ch>, Alison Wang <alison.wang@....com>, 
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Matthias Schiffer <matthias.schiffer@...group.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND 2/2] drm: fsl-dcu: enable PIXCLK on LS1021A

On Wed, Sep 04, 2024 at 01:51:35PM GMT, Alexander Stein wrote:
> From: Matthias Schiffer <matthias.schiffer@...group.com>
> 
> The PIXCLK needs to be enabled in SCFG before accessing certain DCU
> registers, or the access will hang.
> 
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...group.com>
> Signed-off-by: Alexander Stein <alexander.stein@...tq-group.com>
> ---
>  drivers/gpu/drm/fsl-dcu/Kconfig           |  1 +
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 14 ++++++++++++++
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h |  3 +++
>  3 files changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/fsl-dcu/Kconfig b/drivers/gpu/drm/fsl-dcu/Kconfig
> index 5ca71ef87325..c9ee98693b48 100644
> --- a/drivers/gpu/drm/fsl-dcu/Kconfig
> +++ b/drivers/gpu/drm/fsl-dcu/Kconfig
> @@ -8,6 +8,7 @@ config DRM_FSL_DCU
>  	select DRM_PANEL
>  	select REGMAP_MMIO
>  	select VIDEOMODE_HELPERS
> +	select MFD_SYSCON if SOC_LS1021A
>  	help
>  	  Choose this option if you have an Freescale DCU chipset.
>  	  If M is selected the module will be called fsl-dcu-drm.
> 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 90cbd18f096d..283858350961 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> @@ -100,12 +100,26 @@ static void fsl_dcu_irq_uninstall(struct drm_device *dev)
>  static int fsl_dcu_load(struct drm_device *dev, unsigned long flags)
>  {
>  	struct fsl_dcu_drm_device *fsl_dev = dev->dev_private;
> +	struct regmap *scfg;
>  	int ret;
>  
>  	ret = fsl_dcu_drm_modeset_init(fsl_dev);
>  	if (ret < 0)
>  		return dev_err_probe(dev->dev, ret, "failed to initialize mode setting\n");
>  
> +	scfg = syscon_regmap_lookup_by_compatible("fsl,ls1021a-scfg");
> +	if (PTR_ERR(scfg) != -ENODEV) {
> +		/*
> +		 * For simplicity, enable the PIXCLK unconditionally. Disabling
> +		 * the clock in PM or on unload could be implemented as a future
> +		 * improvement.

This decision should be described in the commit message as well, as the
possible drawbacks (e.g. power consumption, stuck picure, etc).

> +		 */
> +		ret = regmap_update_bits(scfg, SCFG_PIXCLKCR, SCFG_PIXCLKCR_PXCEN,
> +					SCFG_PIXCLKCR_PXCEN);
> +		if (ret < 0)
> +			return dev_err_probe(dev->dev, ret, "failed to enable pixclk\n");
> +	}
> +
>  	ret = drm_vblank_init(dev, dev->mode_config.num_crtc);
>  	if (ret < 0) {
>  		dev_err(dev->dev, "failed to initialize vblank\n");
> 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 e2049a0e8a92..566396013c04 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h
> @@ -160,6 +160,9 @@
>  #define FSL_DCU_ARGB4444		12
>  #define FSL_DCU_YUV422			14
>  
> +#define SCFG_PIXCLKCR			0x28
> +#define SCFG_PIXCLKCR_PXCEN		BIT(31)
> +
>  #define VF610_LAYER_REG_NUM		9
>  #define LS1021A_LAYER_REG_NUM		10
>  
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry