mmc: sdhci-xenon: fix 1.8v regulator stabilization

Automatic Clock Gating is a feature used for the power consumption
optimisation. It turned out that during early init phase it may prevent the
stable voltage switch to 1.8V - due to that on some platforms an endless
printout in dmesg can be observed: "mmc1: 1.8V regulator output did not
became stable" Fix the problem by disabling the ACG at very beginning of
the sdhci_init and let that be enabled later.

Fixes: 3a3748d ("mmc: sdhci-xenon: Add Marvell Xenon SDHC core functionality")
Signed-off-by: Alex Leibovich <alexl@marvell.com>
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Cc: stable@vger.kernel.org
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20201211141656.24915-1-mw@semihalf.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: Alex Leibovich

drivers/mmc/host/sdhci-xenon.c

@@ -168,7 +168,12 @@ static void xenon_reset_exit(struct sdhci_host *host,
 	/* Disable tuning request and auto-retuning again */
 	xenon_retune_setup(host);
 
-	xenon_set_acg(host, true);
+	/*
+	 * The ACG should be turned off at the early init time, in order
+	 * to solve a possible issues with the 1.8V regulator stabilization.
+	 * The feature is enabled in later stage.
+	 */
+	xenon_set_acg(host, false);
 
 	xenon_set_sdclk_off_idle(host, sdhc_id, false);