mmc: atmel: Properly fix clock configuration

Timing issue occurs on eMMC not only when modifying the frequency but
also for all the switch command(CMD6). According to the MMC spec waiting
8 clocks after a switch command would be the thing to do.

This patch allows fixing CPU hang observed when trying to changing the
bus width on a eMMC on SAMA5D4.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Tested-by: Marek Vasut <marex@denx.de> # on DENX MA5D4EV
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Andreas Bießmann <andreas.devel@googlemail.com> # on atngw100
Acked-by: Andreas Bießmann <andreas.devel@googlemail.com>
[fixed minor checkpatch warning]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

drivers/mmc/gen_atmel_mci.c

@@ -36,6 +36,7 @@ struct atmel_mci_priv {
 	struct mmc_config	cfg;
 	struct atmel_mci	*mci;
 	unsigned int		initialized:1;
+	unsigned int		curr_clk;
 };
 
 /* Read Atmel MCI IP version */
@@ -91,7 +92,10 @@ static void mci_set_mode(struct mmc *mmc, u32 hz, u32 blklen)
 
 		}
 	}
-
+	if (version >= 0x500)
+		priv->curr_clk = bus_hz / (clkdiv * 2 + clkodd + 2);
+	else
+		priv->curr_clk = (bus_hz / (clkdiv + 1)) / 2;
 	blklen &= 0xfffc;
 
 	mr = MMCI_BF(CLKDIV, clkdiv);
@@ -118,8 +122,6 @@ static void mci_set_mode(struct mmc *mmc, u32 hz, u32 blklen)
 	if (mmc->card_caps & mmc->cfg->host_caps & MMC_MODE_HS)
 		writel(MMCI_BIT(HSMODE), &mci->cfg);
 
-	udelay(50);
-
 	priv->initialized = 1;
 }
 
@@ -323,6 +325,13 @@ mci_send_cmd(struct mmc *mmc, struct mmc_cmd *cmd, struct mmc_data *data)
 		}
 	}
 
+	/*
+	 * After the switch command, wait for 8 clocks before the next
+	 * command
+	 */
+	if (cmd->cmdidx == MMC_CMD_SWITCH)
+		udelay(8*1000000 / priv->curr_clk); /* 8 clk in us */
+
 	return 0;
 }