[PATCH 4/9] mmc: dw_mmc: add voltage switch command flag

[Peng Fan]

Hi Kaustabh,

On Fri, Oct 17, 2025 at 08:54:09PM +0530, Kaustabh Chakraborty wrote:
>During a voltage switch command (CMD11, opcode: SD_CMD_SWITCH_UHS18V),
>certain hosts tend to stop responding to subsequent commands. This is
>addressed by introducing an additional command flag,
>DWMCI_CMD_VOLT_SWITCH.

is there any errata or spec have this information public?

>
>The associated interrupt bit is defined as DWMCI_INTMSK_VOLTSW. This is
>set high when a voltage switch is issued, this needs to be waited for
>and set to low. Implement the same in the timeout loop. Do note that
>since DWMCI_INTMSK_VOLTSW shares the same bit as DWMCI_INTMSK_HTO (bit
>10), the interrupt bit needs to be polled for only if the volt switch
>command is issued.
>
>DWMCI_CMD_VOLT_SWITCH also needs to be set for subsequent clken commands
>after the volt switch. To ensure this, add a boolean member in the host
>private struct (herein named volt_switching), which informs if the last
>command issued was for volt switching or not.
>
>Signed-off-by: Kaustabh Chakraborty <kauschluss at disroot.org>
>---
> drivers/mmc/dw_mmc.c | 15 +++++++++++++--
> include/dwmmc.h      |  4 ++++
> 2 files changed, 17 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/mmc/dw_mmc.c b/drivers/mmc/dw_mmc.c
>index 1aa992c352c3f11ccdd1c02745fa988646952261..94b6641c44c39e67aac453c027d519c0e1580de6 100644
>--- a/drivers/mmc/dw_mmc.c
>+++ b/drivers/mmc/dw_mmc.c
>@@ -419,6 +419,10 @@ static int dwmci_send_cmd_common(struct dwmci_host *host, struct mmc_cmd *cmd,
> 	if (cmd->resp_type & MMC_RSP_CRC)
> 		flags |= DWMCI_CMD_CHECK_CRC;
> 
>+	host->volt_switching = (cmd->cmdidx == SD_CMD_SWITCH_UHS18V);
>+	if (host->volt_switching)
>+		flags |= DWMCI_CMD_VOLT_SWITCH;
>+
> 	flags |= cmd->cmdidx | DWMCI_CMD_START | DWMCI_CMD_USE_HOLD_REG;
> 
> 	debug("Sending CMD%d\n", cmd->cmdidx);
>@@ -427,6 +431,10 @@ static int dwmci_send_cmd_common(struct dwmci_host *host, struct mmc_cmd *cmd,
> 
> 	for (i = 0; i < retry; i++) {
> 		mask = dwmci_readl(host, DWMCI_RINTSTS);
>+		if (host->volt_switching && (mask & DWMCI_INTMSK_VOLTSW)) {
>+			dwmci_writel(host, DWMCI_RINTSTS, DWMCI_INTMSK_VOLTSW);
>+			break;
>+		}
> 		if (mask & DWMCI_INTMSK_CDONE) {
> 			if (!data)
> 				dwmci_writel(host, DWMCI_RINTSTS, mask);
>@@ -508,12 +516,15 @@ static int dwmci_control_clken(struct dwmci_host *host, bool on)
> 	const u32 val = on ? DWMCI_CLKEN_ENABLE | DWMCI_CLKEN_LOW_PWR : 0;
> 	const u32 cmd_only_clk = DWMCI_CMD_PRV_DAT_WAIT | DWMCI_CMD_UPD_CLK;
> 	int i, timeout = 10000;
>-	u32 mask;
>+	u32 flags, mask;
> 
> 	dwmci_writel(host, DWMCI_CLKENA, val);
> 
> 	/* Inform CIU */
>-	dwmci_writel(host, DWMCI_CMD, DWMCI_CMD_START | cmd_only_clk);
>+	flags = DWMCI_CMD_START | cmd_only_clk;
>+	if (host->volt_switching)
>+		flags |= DWMCI_CMD_VOLT_SWITCH;
>+	dwmci_writel(host, DWMCI_CMD, flags);
> 
> 	for (i = 0; i < timeout; i++) {
> 		mask = dwmci_readl(host, DWMCI_RINTSTS);
>diff --git a/include/dwmmc.h b/include/dwmmc.h
>index 639a2d28e7860f2ceb09955ee11550e406fd1bd2..47e3220985e900050d9db9d80e0d45efe6c2e545 100644
>--- a/include/dwmmc.h
>+++ b/include/dwmmc.h
>@@ -72,6 +72,7 @@
> #define DWMCI_INTMSK_RTO	BIT(8)
> #define DWMCI_INTMSK_DRTO	BIT(9)
> #define DWMCI_INTMSK_HTO	BIT(10)
>+#define DWMCI_INTMSK_VOLTSW	BIT(10) /* overlap! */
> #define DWMCI_INTMSK_FRUN	BIT(11)
> #define DWMCI_INTMSK_HLE	BIT(12)
> #define DWMCI_INTMSK_SBE	BIT(13)
>@@ -104,6 +105,7 @@
> #define DWMCI_CMD_ABORT_STOP	BIT(14)
> #define DWMCI_CMD_PRV_DAT_WAIT	BIT(13)
> #define DWMCI_CMD_UPD_CLK	BIT(21)
>+#define DWMCI_CMD_VOLT_SWITCH	BIT(28)
> #define DWMCI_CMD_USE_HOLD_REG	BIT(29)
> #define DWMCI_CMD_START		BIT(31)
> 
>@@ -190,6 +192,7 @@ struct dwmci_idmac_regs {
>  * @cfg:	Internal MMC configuration, for !CONFIG_BLK cases
>  * @fifo_mode:	Use FIFO mode (not DMA) to read and write data
>  * @dma_64bit_address: Whether DMA supports 64-bit address mode or not
>+ * @volt_switching: Whether SD voltage switching is in process or not

Since volt_switching y means in process, I not see it is cleared when it is
not needed. Is this expected?

Thanks,
Peng

>  * @regs:	Registers that can vary for different DW MMC block versions
>  */
> struct dwmci_host {
>@@ -229,6 +232,7 @@ struct dwmci_host {
> 
> 	bool fifo_mode;
> 	bool dma_64bit_address;
>+	bool volt_switching;
> 	const struct dwmci_idmac_regs *regs;
> };
> 
>
>-- 
>2.51.0
>