clk: samsung: exynos5420: Keep top G3D clocks enabled

In Exynos542x/5800 SoCs, the G3D leaf clocks are located in the G3D power
domain. This is similar to the other hardware modules and their power
domains. However there is one thing specific to G3D clocks hierarchy.
Unlike other hardware modules, the G3D clocks hierarchy doesn't have any
gate clock between the TOP part of the hierarchy and the part located in
the power domain and some SoC internal busses are sourced directly from
the TOP muxes. The consequence of this design if the fact that the TOP
part of the hierarchy has to be enabled permanently to ensure proper
operation of the SoC power related components (G3D power domain and
Exynos Power Management Unit for system suspend/resume).

This patch adds an explicit call to clk_prepare_enable() on the last MUX
in the TOP part of G3D clock hierarchy to keep it enabled permanently to
ensure that the internal busses get their clock regardless of the main
G3D clock enablement status.

This fixes following imprecise abort issue observed on Odroid XU3/XU4
after enabling Panfrost driver by commit 1a5a85c564 "ARM: dts: exynos:
Add Mali/GPU node on Exynos5420 and enable it on Odroid XU3/4"):

panfrost 11800000.gpu: clock rate = 400000000
panfrost 11800000.gpu: failed to get regulator: -517
panfrost 11800000.gpu: regulator init failed -517
Power domain G3D disable failed
...
panfrost 11800000.gpu: clock rate = 400000000
8<--- cut here ---
Unhandled fault: imprecise external abort (0x1406) at 0x00000000
pgd = (ptrval)
[00000000] *pgd=00000000
Internal error: : 1406 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 7 PID: 53 Comm: kworker/7:1 Not tainted 5.4.0-rc8-next-20191119-00032-g56f1001191a6 #6923
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
Workqueue: events deferred_probe_work_func
PC is at panfrost_gpu_soft_reset+0x94/0x110
LR is at ___might_sleep+0x128/0x2dc
...
[<c05c231c>] (panfrost_gpu_soft_reset) from [<c05c2704>] (panfrost_gpu_init+0x10/0x67c)
[<c05c2704>] (panfrost_gpu_init) from [<c05c15d0>] (panfrost_device_init+0x158/0x2cc)
[<c05c15d0>] (panfrost_device_init) from [<c05c0cb0>] (panfrost_probe+0x80/0x178)
[<c05c0cb0>] (panfrost_probe) from [<c05cfaa0>] (platform_drv_probe+0x48/0x9c)
[<c05cfaa0>] (platform_drv_probe) from [<c05cd20c>] (really_probe+0x1c4/0x474)
[<c05cd20c>] (really_probe) from [<c05cd694>] (driver_probe_device+0x78/0x1bc)
[<c05cd694>] (driver_probe_device) from [<c05cb374>] (bus_for_each_drv+0x74/0xb8)
[<c05cb374>] (bus_for_each_drv) from [<c05ccfa8>] (__device_attach+0xd4/0x16c)
[<c05ccfa8>] (__device_attach) from [<c05cc110>] (bus_probe_device+0x88/0x90)
[<c05cc110>] (bus_probe_device) from [<c05cc634>] (deferred_probe_work_func+0x4c/0xd0)
[<c05cc634>] (deferred_probe_work_func) from [<c0149df0>] (process_one_work+0x300/0x864)
[<c0149df0>] (process_one_work) from [<c014a3ac>] (worker_thread+0x58/0x5a0)
[<c014a3ac>] (worker_thread) from [<c0151174>] (kthread+0x12c/0x160)
[<c0151174>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20)
Exception stack(0xee03dfb0 to 0xee03dff8)
...
Code: e594300c e5933020 e3130c01 1a00000f (ebefff50).
---[ end trace badde2b74a65a540 ]---

In the above case, the Panfrost driver disables G3D clocks after failure
of getting the needed regulator and return with -EPROVE_DEFER code. This
causes G3D power domain disable failure and then, during second probe
an imprecise abort is triggered due to undefined power domain state.

Fixes: 45f10dabb5 ("clk: samsung: exynos5420: Add SET_RATE_PARENT flag to clocks on G3D path")
Fixes: c9f7567aff ("clk: samsung: exynos542x: Move G3D subsystem clocks to its sub-CMU")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lkml.kernel.org/r/20191216131407.17225-1-m.szyprowski@samsung.com
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/samsung/clk-exynos5420.c

@@ -12,6 +12,7 @@
 #include <linux/clk-provider.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/clk.h>
 
 #include "clk.h"
 #include "clk-cpu.h"
@@ -1646,6 +1647,13 @@ static void __init exynos5x_clk_init(struct device_node *np,
 				     exynos5x_subcmus);
 	}
 
+	/*
+	 * Keep top part of G3D clock path enabled permanently to ensure
+	 * that the internal busses get their clock regardless of the
+	 * main G3D clock enablement status.
+	 */
+	clk_prepare_enable(__clk_lookup("mout_sw_aclk_g3d"));
+
 	samsung_clk_of_add_provider(np, ctx);
 }