Some Realtek USB SD readers with a tray can assert SD_CD even when no
card is present. This can make the MMC core believe a card exists and
trigger unnecessary initialization and suspend/shutdown failures.

Debounce the CD signal and validate a newly detected card by probing for
a response (CMD0 + CMD8/CMD55/CMD1) before reporting it present. Also
treat SD_INT as a removal indication even if SD_CD stays asserted.

Tested: Realtek RTS5129 (0bda:0129), tray inserted, no card (2026-02-24)
Tested: Realtek RTS5129 (0bda:0129), tray + SDXC card, mmcblk0 (2026-02-24)

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
---
 drivers/mmc/host/rtsx_usb_sdmmc.c | 156 ++++++++++++++++++++++++++++--
 1 file changed, 148 insertions(+), 8 deletions(-)

diff --git a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c
index 84674659a84d..ec3eeea78e95 100644
--- a/drivers/mmc/host/rtsx_usb_sdmmc.c
+++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
@@ -19,6 +19,7 @@
 #include <linux/scatterlist.h>
 #include <linux/pm.h>
 #include <linux/pm_runtime.h>
+#include <linux/jiffies.h>
 
 #include <linux/rtsx_usb.h>
 #include <linux/unaligned.h>
@@ -30,6 +31,9 @@
 #define RTSX_USB_USE_LEDS_CLASS
 #endif
 
+#define RTSX_USB_SD_CD_DEBOUNCE_CNT	2
+#define RTSX_USB_SD_INSERT_RETRY_MS	1000
+
 struct rtsx_usb_sdmmc {
 	struct platform_device	*pdev;
 	struct rtsx_ucr	*ucr;
@@ -46,6 +50,8 @@ struct rtsx_usb_sdmmc {
 	bool			card_exist;
 	bool			initial_mode;
 	bool			ddr_mode;
+	u8			cd_debounce;
+	unsigned long		next_insert_check;
 
 	unsigned char		power_mode;
 	u16			ocp_stat;
@@ -72,6 +78,13 @@ static inline void sd_clear_error(struct rtsx_usb_sdmmc *host)
 	rtsx_usb_clear_fsm_err(ucr);
 }
 
+static int sd_set_bus_width(struct rtsx_usb_sdmmc *host,
+			    unsigned char bus_width);
+static int sd_set_timing(struct rtsx_usb_sdmmc *host,
+			 unsigned char timing, bool *ddr_mode);
+static int sd_power_on(struct rtsx_usb_sdmmc *host);
+static int sd_power_off(struct rtsx_usb_sdmmc *host);
+
 #ifdef DEBUG
 static void sd_print_debug_regs(struct rtsx_usb_sdmmc *host)
 {
@@ -768,12 +781,94 @@ static int sdmmc_get_ro(struct mmc_host *mmc)
 	return 0;
 }
 
+static bool sdmmc_validate_insert_locked(struct rtsx_usb_sdmmc *host)
+{
+	struct rtsx_ucr *ucr = host->ucr;
+	struct mmc_command cmd = { };
+	int err = 0;
+	bool probe_powered = false;
+	bool ddr_mode = false;
+
+	/*
+	 * Some readers with a tray assert the mechanical SD_CD pin even when no
+	 * card is present. Only report a card present when it responds to a
+	 * minimal reset/probe sequence, similar to the old rts5139 behavior.
+	 *
+	 * Must be called with ucr->dev_mutex held.
+	 */
+	if (host->power_mode == MMC_POWER_OFF) {
+		err = sd_power_on(host);
+		if (err)
+			return false;
+		probe_powered = true;
+
+		/* Issue clock signals to card for at least 74 clocks. */
+		rtsx_usb_write_register(ucr, SD_BUS_STAT,
+					SD_CLK_TOGGLE_EN, SD_CLK_TOGGLE_EN);
+		usleep_range(200, 400);
+		rtsx_usb_write_register(ucr, SD_BUS_STAT, SD_CLK_TOGGLE_EN, 0);
+	}
+
+	/*
+	 * Ensure the interface is in a safe, legacy / initial-clock mode before
+	 * probing for a response. The MMC core may not have configured ios yet.
+	 */
+	err = sd_set_bus_width(host, MMC_BUS_WIDTH_1);
+	if (err)
+		goto out;
+
+	err = sd_set_timing(host, MMC_TIMING_LEGACY, &ddr_mode);
+	if (err)
+		goto out;
+
+	ucr->cur_clk = 0;
+	err = rtsx_usb_switch_clock(ucr, 400000, SSC_DEPTH_512K,
+				    true, true, false);
+	if (err)
+		goto out;
+
+	cmd.opcode = MMC_GO_IDLE_STATE;
+	cmd.arg = 0;
+	cmd.flags = MMC_RSP_NONE | MMC_CMD_BC;
+	sd_send_cmd_get_rsp(host, &cmd);
+
+	/* SD v2.0+: CMD8 */
+	cmd.opcode = SD_SEND_IF_COND;
+	cmd.arg = 0x1aa;
+	cmd.flags = MMC_RSP_R7 | MMC_CMD_BCR;
+	sd_send_cmd_get_rsp(host, &cmd);
+	if (!cmd.error)
+		goto out;
+
+	/* SD v1.x: CMD55 */
+	cmd.opcode = MMC_APP_CMD;
+	cmd.arg = 0;
+	cmd.flags = MMC_RSP_R1 | MMC_CMD_AC;
+	sd_send_cmd_get_rsp(host, &cmd);
+	if (!cmd.error)
+		goto out;
+
+	/* MMC: CMD1 */
+	cmd.opcode = MMC_SEND_OP_COND;
+	cmd.arg = 0;
+	cmd.flags = MMC_RSP_R3 | MMC_CMD_BCR;
+	sd_send_cmd_get_rsp(host, &cmd);
+
+out:
+	if (probe_powered)
+		sd_power_off(host);
+	return !err && !cmd.error;
+}
+
 static int sdmmc_get_cd(struct mmc_host *mmc)
 {
 	struct rtsx_usb_sdmmc *host = mmc_priv(mmc);
 	struct rtsx_ucr *ucr = host->ucr;
 	int err;
 	u16 val;
+	u8 pend;
+	bool sd_int = false;
+	bool cd_raw = false;
 
 	if (host->host_removal)
 		return -ENOMEDIUM;
@@ -782,28 +877,71 @@ static int sdmmc_get_cd(struct mmc_host *mmc)
 
 	/* Check SD card detect */
 	err = rtsx_usb_get_card_status(ucr, &val);
-
-	mutex_unlock(&ucr->dev_mutex);
-
-	/* Treat failed detection as non-exist */
 	if (err)
-		goto no_card;
+		goto no_card_unlock;
 
 	/* get OCP status */
 	host->ocp_stat = (val >> 4) & 0x03;
 
-	if (val & SD_CD) {
-		host->card_exist = true;
+	cd_raw = !!(val & SD_CD);
+
+	/* Use SD_INT as a reliable removal indication on some tray readers. */
+	err = rtsx_usb_read_register(ucr, CARD_INT_PEND, &pend);
+	if (!err) {
+		sd_int = !!(pend & SD_INT);
+		if (sd_int)
+			rtsx_usb_write_register(ucr, CARD_INT_PEND,
+						SD_INT, SD_INT);
+	}
+
+	if (!cd_raw) {
+		host->cd_debounce = 0;
+		host->next_insert_check = 0;
+		goto no_card_unlock;
+	}
+
+	/*
+	 * rts5139-style: when a card is already known present, treat SD_INT as
+	 * a removal event even if SD_CD stays high (e.g. tray-based readers).
+	 */
+	if (host->card_exist) {
+		if (sd_int) {
+			host->cd_debounce = 0;
+			host->next_insert_check = 0;
+			goto no_card_unlock;
+		}
+		mutex_unlock(&ucr->dev_mutex);
 		return 1;
 	}
 
-no_card:
+	/* Debounce mechanical CD before probing for a response. */
+	if (host->cd_debounce < RTSX_USB_SD_CD_DEBOUNCE_CNT) {
+		host->cd_debounce++;
+		goto no_card_unlock;
+	}
+
+	/* Avoid pounding the bus with probes if CD is stuck asserted. */
+	if (time_before(jiffies, host->next_insert_check))
+		goto no_card_unlock;
+
+	if (!sdmmc_validate_insert_locked(host)) {
+		host->next_insert_check = jiffies +
+			msecs_to_jiffies(RTSX_USB_SD_INSERT_RETRY_MS);
+		goto no_card_unlock;
+	}
+
+	host->card_exist = true;
+	mutex_unlock(&ucr->dev_mutex);
+	return 1;
+
+no_card_unlock:
 	/* clear OCP status */
 	if (host->ocp_stat & (MS_OCP_NOW | MS_OCP_EVER)) {
 		rtsx_usb_write_register(ucr, OCPCTL, MS_OCP_CLEAR, MS_OCP_CLEAR);
 		host->ocp_stat = 0;
 	}
 	host->card_exist = false;
+	mutex_unlock(&ucr->dev_mutex);
 	return 0;
 }
 
@@ -1359,6 +1497,8 @@ static void rtsx_usb_init_host(struct rtsx_usb_sdmmc *host)
 
 	host->power_mode = MMC_POWER_OFF;
 	host->ocp_stat = 0;
+	host->cd_debounce = 0;
+	host->next_insert_check = 0;
 }
 
 static int rtsx_usb_sdmmc_drv_probe(struct platform_device *pdev)
-- 
2.51.0