[PATCH 2/2] clk: qcom: Add a dummy enable function for GX gdsc

[Jordan Crouse <jcrouse@codeaurora.org>]

Most of the time the CPU should not be touching the GX
domain on the GPU except for a very special use case when
the CPU needs to force the GX headswitch off. Add a
dummy enable function for the GX gdsc to simulate success
so that the pm_runtime reference counting is correct.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
---
 drivers/clk/qcom/gpucc-sdm845.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/clk/qcom/gpucc-sdm845.c b/drivers/clk/qcom/gpucc-sdm845.c
index 11222f487a65..7266e9a1d77e 100644
--- a/drivers/clk/qcom/gpucc-sdm845.c
+++ b/drivers/clk/qcom/gpucc-sdm845.c
@@ -131,11 +131,37 @@ static struct gdsc gpu_cx_gdsc = {
 	.flags = VOTABLE,
 };
 
+/*
+ * On SDM845 the GPU GX domain is *almost* entirely controlled by the GMU
+ * running in the CX domain so the CPU doesn't need to know anything about the
+ * GX domain EXCEPT....
+ *
+ * Hardware constraints dictate that the GX be powered down before the CX. If
+ * the GMU crashes it could leave the GX on. In order to successfully bring back
+ * the device the CPU needs to disable the GX headswitch. There being no sane
+ * way to reach in and touch that register from deep inside the GPU driver we
+ * need to set up the infrastructure to be able to ensure that the GPU can
+ * ensure that the GX is off during this super special case. We do this by
+ * defining a GX gdsc with a dummy enable function and a "default" disable
+ * function.
+ *
+ * This allows us to attach with genpd_dev_pm_attach_by_name() in the GPU
+ * driver. During power up, nothing will happen from the CPU (and the GMU will
+ * power up normally but during power down this will ensure that the GX domain
+ * is *really* off - this gives us a semi standard way of doing what we need.
+ */
+static int gx_gdsc_enable(struct generic_pm_domain *domain)
+{
+	/* Do nothing but give genpd the impression that we were successful */
+	return 0;
+}
+
 static struct gdsc gpu_gx_gdsc = {
 	.gdscr = 0x100c,
 	.clamp_io_ctrl = 0x1508,
 	.pd = {
 		.name = "gpu_gx_gdsc",
+		.power_on = gx_gdsc_enable,
 	},
 	.pwrsts = PWRSTS_OFF_ON,
 	.flags = CLAMP_IO | AON_RESET | POLL_CFG_GDSCR,
-- 
2.18.0