mmc: dw_mmc: Don't start commands while busy

This change “mmc: dw_mmc: Don't start commands while busy” (commit 0bdbd0e) in Linux kernel is authored by Doug Anderson <dianders [at]> on Fri Feb 20 12:31:56 2015 -0800.

Description of "mmc: dw_mmc: Don't start commands while busy"

The change “mmc: dw_mmc: Don't start commands while busy” introduces changes as follows.

mmc: dw_mmc: Don't start commands while busy

We've seen problems on some WiFi modules where we seem to send a CMD53
(which requires the data lines) while the module is asserting busy.
We shouldn't do that.

The Designware Databook says that before issuing a new data transfer
command we should check for busy, so that's what we'll do.

We'll leverage the existing dw_mmc knowledge about whether it should
wait for the previous command to finish to know whether we should
check for busy before sending the command.  This means we won't end up
incorrectly waiting for things like CMD52 (SDIO) or CMD13 (SD) which
don't use the data line.

Note that this also has the advantage of making sure that we don't
change the clock while the card is busy, too.

Signed-off-by: Doug Anderson <>
Tested-by: Javier Martinez Canillas <>
Signed-off-by: Jaehoon Chung <>
Signed-off-by: Ulf Hansson <>

Linux kernel releases containing commit 0bdbd0e

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes from "mmc: dw_mmc: Don't start commands while busy"

There are 28 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/mmc/host/dw_mmc.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index d7fca9d799c4..28fb5501aba2 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -102,6 +102,7 @@ struct idmac_desc {
 static bool dw_mci_reset(struct dw_mci *host);
 static bool dw_mci_ctrl_reset(struct dw_mci *host, u32 reset);
+static int dw_mci_card_busy(struct mmc_host *mmc);
 #if defined(CONFIG_DEBUG_FS)
 static int dw_mci_req_show(struct seq_file *s, void *v)
@@ -335,6 +336,31 @@ static u32 dw_mci_prep_stop_abort(struct dw_mci *host, struct mmc_command *cmd)
 	return cmdr;
+static void dw_mci_wait_while_busy(struct dw_mci *host, u32 cmd_flags)
+	unsigned long timeout = jiffies + msecs_to_jiffies(500);
+	/*
+	 * Databook says that before issuing a new data transfer command
+	 * we need to check to see if the card is busy.  Data transfer commands
+	 * all have SDMMC_CMD_PRV_DAT_WAIT set, so we'll key off that.
+	 *
+	 * ...also allow sending for SDMMC_CMD_VOLT_SWITCH where busy is
+	 * expected.
+	 */
+	if ((cmd_flags & SDMMC_CMD_PRV_DAT_WAIT) &&
+	    !(cmd_flags & SDMMC_CMD_VOLT_SWITCH)) {
+		while (mci_readl(host, STATUS) & SDMMC_STATUS_BUSY) {
+			if (time_after(jiffies, timeout)) {
+				/* Command will fail; we'll pass error then */
+				dev_err(host->dev, "Busy; trying anyway\n");
+				break;
+			}
+			udelay(10);
+		}
+	}
 static void dw_mci_start_command(struct dw_mci *host,
 				 struct mmc_command *cmd, u32 cmd_flags)
@@ -345,6 +371,7 @@ static void dw_mci_start_command(struct dw_mci *host,
 	mci_writel(host, CMDARG, cmd->arg);
+	dw_mci_wait_while_busy(host, cmd_flags);
 	mci_writel(host, CMD, cmd_flags | SDMMC_CMD_START);
@@ -876,6 +903,7 @@ static void mci_send_cmd(struct dw_mci_slot *slot, u32 cmd, u32 arg)
 	mci_writel(host, CMDARG, arg);
+	dw_mci_wait_while_busy(host, cmd);
 	mci_writel(host, CMD, SDMMC_CMD_START | cmd);
 	while (time_before(jiffies, timeout)) {

The commit for this change in Linux stable tree is 0bdbd0e (patch).

Last modified: 2020/02/10