[PATCH v6 2/3] mmc: dw_mmc: Honor requests to set the clock to 0 (turn off clock)

[Doug Anderson <dianders@chromium.org>]

Previously the dw_mmc driver would ignore any requests to disable the
card's clock.  This doesn't seem like a good thing in general, but had
one extra bad side effect in the following situtation:
* mmc core would set clk to 400kHz at boot time while initting
* mmc core would set clk to 0 since no card, but it would be ignored.
* suspend to ram and resume; clocks in the dw_mmc IP block are now 0
  but dw_mmc thinks that they're 400kHz (it ignored the set to 0).
* insert card
* mmc core would set clk to 400kHz which would be considered a no-op.

Note that if there is no card in the slot and we do a suspend/resume
cycle, we _do_ still end up with differences in a dw_mmc register
dump, but the differences are clock related and we've got the clock
disabled both before and after, so this should be OK.

Signed-off-by: Doug Anderson <dianders@chromium.org>
---
Changes in v6:
- Replaces previous pathes that ensured saving/restoring clocks.

 drivers/mmc/host/dw_mmc.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index ee5f167..f6c7545 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -635,7 +635,11 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
 	u32 div;
 	u32 clk_en_a;
 
-	if (slot->clock != host->current_speed || force_clkinit) {
+	if (slot->clock == 0) {
+		mci_writel(host, CLKENA, 0);
+		mci_send_cmd(slot,
+			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
+	} else if (slot->clock != host->current_speed || force_clkinit) {
 		div = host->bus_hz / slot->clock;
 		if (host->bus_hz % slot->clock && host->bus_hz > slot->clock)
 			/*
@@ -675,9 +679,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
 		/* inform CIU */
 		mci_send_cmd(slot,
 			     SDMMC_CMD_UPD_CLK | SDMMC_CMD_PRV_DAT_WAIT, 0);
-
-		host->current_speed = slot->clock;
 	}
+	host->current_speed = slot->clock;
 
 	/* Set the current slot bus width */
 	mci_writel(host, CTYPE, (slot->ctype << slot->id));
@@ -807,13 +810,11 @@ static void dw_mci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 
 	mci_writel(slot->host, UHS_REG, regs);
 
-	if (ios->clock) {
-		/*
-		 * Use mirror of ios->clock to prevent race with mmc
-		 * core ios update when finding the minimum.
-		 */
-		slot->clock = ios->clock;
-	}
+	/*
+	 * Use mirror of ios->clock to prevent race with mmc
+	 * core ios update when finding the minimum.
+	 */
+	slot->clock = ios->clock;
 
 	if (drv_data && drv_data->set_ios)
 		drv_data->set_ios(slot->host, ios);
-- 
1.8.3