linux-kernel - Re: [PATCH] drm: fsl-dcu: enable PIXCLK on LS1021A

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Date:   Fri, 21 Aug 2020 15:41:09 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        sboyd@...nel.org, mturquette@...libre.com
Cc:     Alison Wang <alison.wang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: fsl-dcu: enable PIXCLK on LS1021A

Hi Matthias,

On 2020-08-20 12:58, Matthias Schiffer wrote:
> The PIXCLK needs to be enabled in SCFG before accessing the DCU on LS1021A,
> or the access will hang.

Hm, this seems a rather ad-hoc access to SCFG from the DCU. We do
support a pixel clock in the device tree bindings of fsl-dcu, so ideally
we should enable the pixel clock through the clock framework.

On the other hand, I guess that would mean adding a clock driver to flip
a single bit, which seems a bit excessive too.

I'd like a second opinion on that. Adding clk framework maintainers.

--
Stefan

> 
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
>  drivers/gpu/drm/fsl-dcu/Kconfig           |  1 +
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 25 +++++++++++++++++++++++
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h |  3 +++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/fsl-dcu/Kconfig b/drivers/gpu/drm/fsl-dcu/Kconfig
> index d7dd8ba90e3a..9e5a35e7c00c 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 abbc1ddbf27f..8a7556655581 100644
> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c
> @@ -51,6 +51,23 @@ static const struct regmap_config fsl_dcu_regmap_config = {
>  	.volatile_reg = fsl_dcu_drm_is_volatile_reg,
>  };
>  
> +static int fsl_dcu_scfg_config_ls1021a(struct device_node *np)
> +{
> +	struct regmap *scfg;
> +
> +	scfg = syscon_regmap_lookup_by_compatible("fsl,ls1021a-scfg");
> +	if (IS_ERR(scfg))
> +		return PTR_ERR(scfg);
> +
> +	/*
> +	 * For simplicity, enable the PIXCLK unconditionally. It might
> +	 * be possible to disable the clock in PM or on unload as a future
> +	 * improvement.
> +	 */
> +	return regmap_update_bits(scfg, SCFG_PIXCLKCR, SCFG_PIXCLKCR_PXCEN,
> +				  SCFG_PIXCLKCR_PXCEN);
> +}
> +
>  static void fsl_dcu_irq_uninstall(struct drm_device *dev)
>  {
>  	struct fsl_dcu_drm_device *fsl_dev = dev->dev_private;
> @@ -70,6 +87,14 @@ static int fsl_dcu_load(struct drm_device *dev,
> unsigned long flags)
>  		return ret;
>  	}
>  
> +	if (of_device_is_compatible(fsl_dev->np, "fsl,ls1021a-dcu")) {
> +		ret = fsl_dcu_scfg_config_ls1021a(fsl_dev->np);
> +		if (ret < 0) {
> +			dev_err(dev->dev, "failed to enable pixclk\n");
> +			goto done;
> +		}
> +	}
> +
>  	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