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

[Stefan Agner]

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@xxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
---
 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;
 
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 {
-- 
2.7.0