clk: qcom: gpucc: Add support for GX GDSC for SC7180

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 the GX domain for that use case.  As part of
this add a dummy enable function for the GX gdsc to simulate success
so that the pm_runtime reference counting is correct.  This matches
what was done in sdm845 in commit 85a3d920d3 ("clk: qcom: Add a
dummy enable function for GX gdsc").

Signed-off-by: Taniya Das <tdas@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lkml.kernel.org/r/1581307266-26989-2-git-send-email-tdas@codeaurora.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/qcom/gpucc-sc7180.c

@@ -170,8 +170,45 @@ static struct gdsc cx_gdsc = {
 	.flags = VOTABLE,
 };
 
+/*
+ * On SC7180 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 gx_gdsc = {
+	.gdscr = 0x100c,
+	.clamp_io_ctrl = 0x1508,
+	.pd = {
+		.name = "gx_gdsc",
+		.power_on = gx_gdsc_enable,
+	},
+	.pwrsts = PWRSTS_OFF_ON,
+	.flags = CLAMP_IO,
+};
+
 static struct gdsc *gpu_cc_sc7180_gdscs[] = {
 	[CX_GDSC] = &cx_gdsc,
+	[GX_GDSC] = &gx_gdsc,
 };
 
 static struct clk_regmap *gpu_cc_sc7180_clocks[] = {