[PATCH v3] drm/etnaviv: add optional reset support

[LECOINTRE Philippe <philippe.lecointre@thalesgroup.com>]

Add optional reset support which is mentioned in vivante,gc.yaml to
allow the driver to work on SoCs whose reset signal is asserted by default

Signed-off-by: Philippe Lecointre <philippe.lecointre@thalesgroup.com>
Reviewed-by: Simon Lenain <simon.lenain@thalesgroup.com>
---
v3:
- Rework to match initial feedback
---
 drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 37 +++++++++++++++++++++++++++
 drivers/gpu/drm/etnaviv/etnaviv_gpu.h |  1 +
 2 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
index 2d4c112ce033..1961ebac315a 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
@@ -13,6 +13,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/regulator/consumer.h>
+#include <linux/reset.h>
 #include <linux/thermal.h>
 
 #include "etnaviv_cmdbuf.h"
@@ -172,6 +173,25 @@ int etnaviv_gpu_get_param(struct etnaviv_gpu *gpu, u32 param, u64 *value)
 	return 0;
 }
 
+static int etnaviv_gpu_reset_deassert(struct etnaviv_gpu *gpu)
+{
+	int ret;
+
+	/* 32 core clock cycles (slowest clock) required before deassertion */
+	/* 1 microsecond might match all implementations without computation */
+	usleep_range(1, 2);
+
+	ret = reset_control_deassert(gpu->rst);
+	if (ret)
+		return ret;
+
+	/* 128 core clock cycles (slowest clock) required before any activity on AHB */
+	/* 1 microsecond might match all implementations without computation */
+	usleep_range(1, 2);
+
+	return 0;
+}
+
 static inline bool etnaviv_is_model_rev(struct etnaviv_gpu *gpu, u32 model, u32 revision)
 {
 	return gpu->identity.model == model &&
@@ -799,6 +819,12 @@ int etnaviv_gpu_init(struct etnaviv_gpu *gpu)
 		goto pm_put;
 	}
 
+	ret = etnaviv_gpu_reset_deassert(gpu);
+	if (ret) {
+		dev_err(gpu->dev, "GPU reset deassert failed\n");
+		goto fail;
+	}
+
 	etnaviv_hw_identify(gpu);
 
 	if (gpu->identity.model == 0) {
@@ -1860,6 +1886,17 @@ static int etnaviv_gpu_platform_probe(struct platform_device *pdev)
 	if (IS_ERR(gpu->mmio))
 		return PTR_ERR(gpu->mmio);
 
+
+	/* Get Reset: */
+	gpu->rst = devm_reset_control_get_optional_exclusive(&pdev->dev, NULL);
+	if (IS_ERR(gpu->rst))
+		return dev_err_probe(dev, PTR_ERR(gpu->rst),
+				     "failed to get reset\n");
+
+	err = reset_control_assert(gpu->rst);
+	if (err)
+		return dev_err_probe(dev, err, "failed to assert reset\n");
+
 	/* Get Interrupt: */
 	gpu->irq = platform_get_irq(pdev, 0);
 	if (gpu->irq < 0)
diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
index 4d8a7d48ade3..0985ea548b82 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.h
@@ -158,6 +158,7 @@ struct etnaviv_gpu {
 	struct clk *clk_reg;
 	struct clk *clk_core;
 	struct clk *clk_shader;
+	struct reset_control *rst;
 
 	unsigned int freq_scale;
 	unsigned int fe_waitcycles;
-- 
2.19.1