clk: qcom: gdsc: Fix the handling of PWRSTS_RET support

GDSCs cannot be transitioned into a Retention state in SW.
When either the RETAIN_MEM bit, or both the RETAIN_MEM and
RETAIN_PERIPH bits are set, and the GDSC is left ON, the HW
takes care of retaining the memory/logic for the domain when
the parent domain transitions to power collapse/power off state.

On some platforms where the parent domains lowest power state
itself is Retention, just leaving the GDSC in ON (without any
RETAIN_MEM/RETAIN_PERIPH bits being set) will also transition
it to Retention.

The existing logic handling the PWRSTS_RET seems to set the
RETAIN_MEM/RETAIN_PERIPH bits if the cxcs offsets are specified
but then explicitly turns the GDSC OFF as part of _gdsc_disable().
Fix that by leaving the GDSC in ON state.
Signed-off-by: Rajendra Nayak <quic_rjendra@quicinc.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220920111517.10407-1-quic_rjendra@quicinc.com

drivers/clk/qcom/gdsc.c

@@ -368,6 +368,16 @@ static int _gdsc_disable(struct gdsc *sc)
 	if (sc->pwrsts & PWRSTS_OFF)
 		gdsc_clear_mem_on(sc);
 
+	/*
+	 * If the GDSC supports only a Retention state, apart from ON,
+	 * leave it in ON state.
+	 * There is no SW control to transition the GDSC into
+	 * Retention state. This happens in HW when the parent
+	 * domain goes down to a Low power state
+	 */
+	if (sc->pwrsts == PWRSTS_RET_ON)
+		return 0;
+
 	ret = gdsc_toggle_logic(sc, GDSC_OFF);
 	if (ret)
 		return ret;

drivers/clk/qcom/gdsc.h

@@ -49,6 +49,11 @@ struct gdsc {
 	const u8			pwrsts;
 /* Powerdomain allowable state bitfields */
 #define PWRSTS_OFF		BIT(0)
+/*
+ * There is no SW control to transition a GDSC into
+ * PWRSTS_RET. This happens in HW when the parent
+ * domain goes down to a low power state
+ */
 #define PWRSTS_RET		BIT(1)
 #define PWRSTS_ON		BIT(2)
 #define PWRSTS_OFF_ON		(PWRSTS_OFF | PWRSTS_ON)