From: MIIX 3-1030 field investigation
Subject: [PATCH] staging: r8723bs: add opt-in legacy SDIO timing workaround

The Lenovo MIIX 3-1030 (DMI board Martini, RTL8723BS 024c:b723 on
INT33BB:00 UID 2) can negotiate SDIO high-speed mode successfully while
all subsequent host-to-card CMD53 data writes fail with CRC errors.

Add two opt-in workarounds:

  force_sdio_legacy=1
    Clear SDIO_SPEED_EHS before the first Realtek I/O operation and put
    the host into MMC_TIMING_LEGACY at 25 MHz.

  force_cmd52_write32=1
    Use four CMD52 byte writes for aligned 32-bit register writes. Bulk
    data and the transmit FIFO continue to use CMD53.

This patch was developed and tested against Ubuntu's 7.0.0-28 kernel.
It may need context changes for other kernel versions.

diff --git a/drivers/staging/rtl8723bs/hal/sdio_ops.c b/drivers/staging/rtl8723bs/hal/sdio_ops.c
index c9cb20c61a2b..8c46230ac874 100644
--- a/drivers/staging/rtl8723bs/hal/sdio_ops.c
+++ b/drivers/staging/rtl8723bs/hal/sdio_ops.c
@@ -7,6 +7,11 @@
 #include <drv_types.h>
 #include <rtl8723b_hal.h>
 
+static bool force_cmd52_write32;
+module_param(force_cmd52_write32, bool, 0644);
+MODULE_PARM_DESC(force_cmd52_write32,
+		 "Use four CMD52 byte writes instead of a CMD53 32-bit write");
+
 /*  */
 /*  Description: */
 /*	The following mapping is for SDIO host local register space. */
@@ -290,9 +295,11 @@ static s32 sdio_write32(struct intf_hdl *intfhdl, u32 addr, u32 val)
 
 	/*  4 bytes alignment */
 	shift = ftaddr & 0x3;
-	if (shift == 0) {
+	if (shift == 0 && !force_cmd52_write32) {
 		sd_write32(intfhdl, ftaddr, val, &err);
 	} else {
+		if (force_cmd52_write32)
+			pr_info_once("r8723bs: forcing 32-bit SDIO writes through CMD52\n");
 		le_tmp = cpu_to_le32(val);
 		err = sd_cmd52_write(intfhdl, ftaddr, 4, (u8 *)&le_tmp);
 	}
diff --git a/drivers/staging/rtl8723bs/os_dep/sdio_intf.c b/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
index d664e254912cf..61c2aba9bd830 100644
--- a/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
+++ b/drivers/staging/rtl8723bs/os_dep/sdio_intf.c
@@ -7,6 +7,14 @@
 #include <drv_types.h>
 #include <hal_btcoex.h>
 #include <linux/jiffies.h>
+#include <linux/mmc/card.h>
+#include <linux/mmc/host.h>
+#include <linux/mmc/sdio.h>
+
+static bool force_sdio_legacy;
+module_param(force_sdio_legacy, bool, 0444);
+MODULE_PARM_DESC(force_sdio_legacy,
+		 "Disable SDIO high speed and use legacy 25 MHz timing");
 
 #ifndef dev_to_sdio_func
 #define dev_to_sdio_func(d)     container_of(d, struct sdio_func, dev)
@@ -33,6 +41,57 @@ static const struct dev_pm_ops rtw_sdio_pm_ops = {
 	.resume	= rtw_sdio_resume,
 };
 
+static int rtw_force_sdio_legacy(struct sdio_func *func)
+{
+	struct mmc_host *host = func->card->host;
+	unsigned int old_quirks;
+	u8 speed;
+	u8 new_speed;
+	unsigned int old_clock;
+	unsigned int old_timing;
+	int err = 0;
+
+	if (!force_sdio_legacy)
+		return 0;
+
+	/* Reverse mmc/core/sdio.c:mmc_sdio_enable_hs() before Realtek I/O. */
+	sdio_claim_host(func);
+	speed = sdio_f0_readb(func, SDIO_CCCR_SPEED, &err);
+	if (err)
+		goto release;
+
+	new_speed = speed & ~SDIO_SPEED_EHS;
+	if (new_speed != speed) {
+		old_quirks = func->card->quirks;
+		func->card->quirks |= MMC_QUIRK_LENIENT_FN0;
+		sdio_f0_writeb(func, new_speed, SDIO_CCCR_SPEED, &err);
+		func->card->quirks = old_quirks;
+		if (err)
+			goto release;
+	}
+
+	old_clock = host->ios.clock;
+	old_timing = host->ios.timing;
+	host->ios.timing = MMC_TIMING_LEGACY;
+	host->ios.clock = min(host->f_max, 25000000U);
+	host->ops->set_ios(host, &host->ios);
+
+release:
+	sdio_release_host(func);
+	if (err) {
+		dev_err(&func->dev,
+			"failed to force legacy SDIO timing at CCCR_SPEED (%d)\n",
+			err);
+		return err;
+	}
+
+	dev_info(&func->dev,
+		 "forced legacy SDIO (CCCR_SPEED %#02x -> %#02x, timing %u -> %u, clock %u -> %u)\n",
+		 speed, new_speed, old_timing, host->ios.timing,
+		 old_clock, host->ios.clock);
+	return 0;
+}
+
 static struct sdio_driver rtl8723bs_sdio_driver = {
 	.probe = rtw_drv_init,
 	.remove = rtw_dev_remove,
@@ -349,6 +408,10 @@ static int rtw_drv_init(
 	struct adapter *if1 = NULL;
 	struct dvobj_priv *dvobj;
 
+	status = rtw_force_sdio_legacy(func);
+	if (status)
+		goto exit;
+
 	dvobj = sdio_dvobj_init(func);
 	if (!dvobj)
 		goto exit;
-- 
2.46.0