Implement voltage switch callback (shamelessly copied from sunxi mmc
driver). This allow, with the appropriate tuning function, to use
SD ultra high speed modes.

Reviewed-by: Kevin Hilman <khil...@baylibre.com>
Signed-off-by: Jerome Brunet <jbru...@baylibre.com>
---
 drivers/mmc/host/meson-gx-mmc.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
index df1ac96bd0db..3167f561e1a6 100644
--- a/drivers/mmc/host/meson-gx-mmc.c
+++ b/drivers/mmc/host/meson-gx-mmc.c
@@ -1050,6 +1050,28 @@ static int meson_mmc_card_busy(struct mmc_host *mmc)
        return !(FIELD_GET(STATUS_DATI, regval) & 0xf);
 }
 
+static int meson_mmc_voltage_switch(struct mmc_host *mmc, struct mmc_ios *ios)
+{
+       /* vqmmc regulator is available */
+       if (!IS_ERR(mmc->supply.vqmmc)) {
+               /*
+                * The usual amlogic setup uses a GPIO to switch from one
+                * regulator to the other. While the voltage ramp up is
+                * pretty fast, care must be taken when switching from 3.3v
+                * to 1.8v. Please make sure the regulator framework is aware
+                * of your own regulator constraints
+                */
+               return mmc_regulator_set_vqmmc(mmc, ios);
+
+       }
+
+       /* no vqmmc regulator, assume fixed regulator at 3/3.3V */
+       if (ios->signal_voltage == MMC_SIGNAL_VOLTAGE_330)
+               return 0;
+
+       return -EINVAL;
+}
+
 static const struct mmc_host_ops meson_mmc_ops = {
        .request        = meson_mmc_request,
        .set_ios        = meson_mmc_set_ios,
@@ -1058,6 +1080,7 @@ static const struct mmc_host_ops meson_mmc_ops = {
        .post_req       = meson_mmc_post_req,
        .execute_tuning = meson_mmc_execute_tuning,
        .card_busy      = meson_mmc_card_busy,
+       .start_signal_voltage_switch = meson_mmc_voltage_switch,
 };
 
 static int meson_mmc_probe(struct platform_device *pdev)
-- 
2.9.5

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