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

[Kaustabh Chakraborty <kauschluss@disroot.org>]

On 2025-10-22 08:14, Peng Fan wrote:
> 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?

I'm not aware of any. However, this behavior is found in the Linux 
kernel
driver. See commit 0173055842cd1 ("mmc: dw_mmc: Support voltage 
changes").
The state tracking in the kernel is however much more complex.

> 
>> 
>> 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@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);

[1]

>> +	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?

See [1] marked above. Its enabled when SD_CMD_SWITCH_UHS18V is the 
opcode,
disabled otherwise.

> 
> 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
>>