drm: fsl-dcu: enable PIXCLK on LS1021A

The PIXCLK needs to be enabled in SCFG before accessing certain DCU
registers, or the access will hang. For simplicity, the PIXCLK is enabled
unconditionally, resulting in increased power consumption.

Signed-off-by: Matthias Schiffer <[e-mail]>
Signed-off-by: Alexander Stein <[e-mail]>
Fixes: 109eee2f2a18 ("drm/layerscape: Add Freescale DCU DRM driver")
Acked-by: Dmitry Baryshkov <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/fsl-dcu/Kconfig

···
 	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.

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c

···
 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,
+		 * resulting in increased power consumption. Disabling
+		 * the clock in PM or on unload could be implemented as
+		 * a future improvement.
+		 */
+		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) {

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.h

···
 #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