[PATCH v2 1/2] drm/sun4i: backend: Make sure we enforce the clock rate

[Maxime Ripard]

The backend needs to run at 300MHz to be functional. This was done so far
using assigned-clocks in the device tree, but that is easy to forget, and
dosen't provide any other guarantee than the rate is going to be roughly
the one requested at probe time.

Therefore it's pretty fragile, so let's just use the exclusive clock API to
enforce it.

Signed-off-by: Maxime Ripard <maxime at cerno.tech>

---

Changes from v1:
  - Add test on the clk_set_rate_exclusive return value
---
 drivers/gpu/drm/sun4i/sun4i_backend.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
index 4e29f4fe4a05..072ea113e6be 100644
--- a/drivers/gpu/drm/sun4i/sun4i_backend.c
+++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
@@ -856,6 +856,13 @@ static int sun4i_backend_bind(struct device *dev, struct device *master,
 		ret = PTR_ERR(backend->mod_clk);
 		goto err_disable_bus_clk;
 	}
+
+	ret = clk_set_rate_exclusive(backend->mod_clk, 300000000);
+	if (ret) {
+		dev_err(dev, "Couldn't set the module clock frequency\n");
+		goto err_disable_bus_clk;
+	}
+
 	clk_prepare_enable(backend->mod_clk);
 
 	backend->ram_clk = devm_clk_get(dev, "ram");
@@ -932,6 +939,7 @@ static int sun4i_backend_bind(struct device *dev, struct device *master,
 err_disable_ram_clk:
 	clk_disable_unprepare(backend->ram_clk);
 err_disable_mod_clk:
+	clk_rate_exclusive_put(backend->mod_clk);
 	clk_disable_unprepare(backend->mod_clk);
 err_disable_bus_clk:
 	clk_disable_unprepare(backend->bus_clk);
@@ -952,6 +960,7 @@ static void sun4i_backend_unbind(struct device *dev, struct device *master,
 		sun4i_backend_free_sat(dev);
 
 	clk_disable_unprepare(backend->ram_clk);
+	clk_rate_exclusive_put(backend->mod_clk);
 	clk_disable_unprepare(backend->mod_clk);
 	clk_disable_unprepare(backend->bus_clk);
 	reset_control_assert(backend->reset);
-- 
2.24.1