[PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[rui_feng]

From: rui_feng <rui_feng@realsil.com.cn>

RTS5261 support legacy SD mode and SD Express mode.
In SD7.x, SD association introduce SD Express as a new mode.
SD Express mode is distinguished by CMD8.
Therefore, CMD8 has new bit for SD Express.
SD Express is based on PCIe/NVMe.
RTS5261 uses CMD8 to switch to SD Express mode.

Signed-off-by: rui_feng <rui_feng@realsil.com.cn>
---
v2: remove config option MISC_RTSX_PCI_SD_EXPRESS 
---

 drivers/misc/cardreader/rts5261.c  |  5 ++++
 drivers/misc/cardreader/rts5261.h  | 23 ----------------
 drivers/misc/cardreader/rtsx_pcr.c |  5 ++++
 drivers/mmc/core/sd_ops.c          |  9 ++++++-
 drivers/mmc/host/rtsx_pci_sdmmc.c  | 43 ++++++++++++++++++++++++++++++
 include/linux/mmc/host.h           |  1 +
 include/linux/rtsx_pci.h           | 27 +++++++++++++++++++
 7 files changed, 89 insertions(+), 24 deletions(-)

diff --git a/drivers/misc/cardreader/rts5261.c b/drivers/misc/cardreader/rts5261.c
index 547db5ffd3f6..c6280bb7a67b 100644
--- a/drivers/misc/cardreader/rts5261.c
+++ b/drivers/misc/cardreader/rts5261.c
@@ -759,8 +759,12 @@ void rts5261_init_params(struct rtsx_pcr *pcr)
 {
 	struct rtsx_cr_option *option = &pcr->option;
 	struct rtsx_hw_param *hw_param = &pcr->hw_param;
+	u8 val;
 
 	pcr->extra_caps = EXTRA_CAPS_SD_SDR50 | EXTRA_CAPS_SD_SDR104;
+	rtsx_pci_read_register(pcr, RTS5261_FW_STATUS, &val);
+	if (!(val & RTS5261_EXPRESS_LINK_FAIL_MASK))
+		pcr->extra_caps |= EXTRA_CAPS_SD_EXPRESS;
 	pcr->num_slots = 1;
 	pcr->ops = &rts5261_pcr_ops;
 
@@ -791,6 +795,7 @@ void rts5261_init_params(struct rtsx_pcr *pcr)
 	option->ltr_l1off_snooze_sspwrgate = 0x78;
 	option->dev_aspm_mode = DEV_ASPM_DYNAMIC;
 
+	hw_param->interrupt_en |= DELINK_INT_EN;
 	option->ocp_en = 1;
 	hw_param->interrupt_en |= SD_OC_INT_EN;
 	hw_param->ocp_glitch =  SD_OCP_GLITCH_800U;
diff --git a/drivers/misc/cardreader/rts5261.h b/drivers/misc/cardreader/rts5261.h
index ebfdd236a553..8d80f0d5d5d6 100644
--- a/drivers/misc/cardreader/rts5261.h
+++ b/drivers/misc/cardreader/rts5261.h
@@ -65,23 +65,6 @@
 #define RTS5261_FW_EXPRESS_TEST_MASK	(0x01<<0)
 #define RTS5261_FW_EA_MODE_MASK		(0x01<<5)
 
-/* FW config register */
-#define RTS5261_FW_CFG0			0xFF54
-#define RTS5261_FW_ENTER_EXPRESS	(0x01<<0)
-
-#define RTS5261_FW_CFG1			0xFF55
-#define RTS5261_SYS_CLK_SEL_MCU_CLK	(0x01<<7)
-#define RTS5261_CRC_CLK_SEL_MCU_CLK	(0x01<<6)
-#define RTS5261_FAKE_MCU_CLOCK_GATING	(0x01<<5)
-/*MCU_bus_mode_sel: 0=real 8051 1=fake mcu*/
-#define RTS5261_MCU_BUS_SEL_MASK	(0x01<<4)
-/*MCU_clock_sel:VerA 00=aux16M 01=aux400K 1x=REFCLK100M*/
-/*MCU_clock_sel:VerB 00=aux400K 01=aux16M 10=REFCLK100M*/
-#define RTS5261_MCU_CLOCK_SEL_MASK	(0x03<<2)
-#define RTS5261_MCU_CLOCK_SEL_16M	(0x01<<2)
-#define RTS5261_MCU_CLOCK_GATING	(0x01<<1)
-#define RTS5261_DRIVER_ENABLE_FW	(0x01<<0)
-
 /* FW status register */
 #define RTS5261_FW_STATUS		0xFF56
 #define RTS5261_EXPRESS_LINK_FAIL_MASK	(0x01<<7)
@@ -121,12 +104,6 @@
 #define RTS5261_DV3318_19		(0x04<<4)
 #define RTS5261_DV3318_33		(0x07<<4)
 
-#define RTS5261_LDO1_CFG0		0xFF72
-#define RTS5261_LDO1_OCP_THD_MASK	(0x07<<5)
-#define RTS5261_LDO1_OCP_EN		(0x01<<4)
-#define RTS5261_LDO1_OCP_LMT_THD_MASK	(0x03<<2)
-#define RTS5261_LDO1_OCP_LMT_EN		(0x01<<1)
-
 /* CRD6603-433 190319 request changed */
 #define RTS5261_LDO1_OCP_THD_740	(0x00<<5)
 #define RTS5261_LDO1_OCP_THD_800	(0x01<<5)
diff --git a/drivers/misc/cardreader/rtsx_pcr.c b/drivers/misc/cardreader/rtsx_pcr.c
index 06038b325b02..4cdc45fdf9b8 100644
--- a/drivers/misc/cardreader/rtsx_pcr.c
+++ b/drivers/misc/cardreader/rtsx_pcr.c
@@ -1026,6 +1026,11 @@ static irqreturn_t rtsx_pci_isr(int irq, void *dev_id)
 		} else {
 			pcr->card_removed |= SD_EXIST;
 			pcr->card_inserted &= ~SD_EXIST;
+			if (PCI_PID(pcr) == PID_5261) {
+				rtsx_pci_write_register(pcr, RTS5261_FW_STATUS,
+					RTS5261_EXPRESS_LINK_FAIL_MASK, 0);
+				pcr->extra_caps |= EXTRA_CAPS_SD_EXPRESS;
+			}
 		}
 		pcr->dma_error_count = 0;
 	}
diff --git a/drivers/mmc/core/sd_ops.c b/drivers/mmc/core/sd_ops.c
index 22bf528294b9..7c70d267644b 100644
--- a/drivers/mmc/core/sd_ops.c
+++ b/drivers/mmc/core/sd_ops.c
@@ -171,7 +171,14 @@ int mmc_send_if_cond(struct mmc_host *host, u32 ocr)
 	 * SD 1.0 cards.
 	 */
 	cmd.opcode = SD_SEND_IF_COND;
-	cmd.arg = ((ocr & 0xFF8000) != 0) << 8 | test_pattern;
+	/*
+	 * Host asks card's PCIe availability
+	 * if PCIe interface is supported by host.
+	 */
+	if ((ocr & 0xFF8000) && (host->caps2 & MMC_CAP2_SD_EXPRESS))
+		cmd.arg = 0x31 << 8 | test_pattern;
+	else
+		cmd.arg = ((ocr & 0xFF8000) != 0) << 8 | test_pattern;
 	cmd.flags = MMC_RSP_SPI_R7 | MMC_RSP_R7 | MMC_CMD_BCR;
 
 	err = mmc_wait_for_cmd(host, &cmd, 0);
diff --git a/drivers/mmc/host/rtsx_pci_sdmmc.c b/drivers/mmc/host/rtsx_pci_sdmmc.c
index bd50935dc37d..87ad75b253eb 100644
--- a/drivers/mmc/host/rtsx_pci_sdmmc.c
+++ b/drivers/mmc/host/rtsx_pci_sdmmc.c
@@ -219,6 +219,7 @@ static void sd_send_cmd_get_rsp(struct realtek_pci_sdmmc *host,
 	int rsp_type;
 	int stat_idx;
 	bool clock_toggled = false;
+	u32 relink_time, val;
 
 	dev_dbg(sdmmc_dev(host), "%s: SD/MMC CMD %d, arg = 0x%08x\n",
 			__func__, cmd_idx, arg);
@@ -322,6 +323,44 @@ static void sd_send_cmd_get_rsp(struct realtek_pci_sdmmc *host,
 	if (err && clock_toggled)
 		rtsx_pci_write_register(pcr, SD_BUS_STAT,
 				SD_CLK_TOGGLE_EN | SD_CLK_FORCE_STOP, 0);
+
+	/*
+	 * If card has PCIe availability and WP if off,
+	 * reader switch to PCIe mode.
+	 */
+	val = rtsx_pci_readl(pcr, RTSX_BIPR);
+	if (cmd->opcode == 8 && ((cmd->resp[0] >> 8) & 0x10)
+		&& !(val & SD_WRITE_PROTECT)) {
+		/* Set relink_time for changing to PCIe card */
+		relink_time = 0x8FFF;
+
+		rtsx_pci_write_register(pcr, 0xFF01, 0xFF, relink_time);
+		rtsx_pci_write_register(pcr, 0xFF02, 0xFF, relink_time >> 8);
+		rtsx_pci_write_register(pcr, 0xFF03, 0x01, relink_time >> 16);
+
+		rtsx_pci_write_register(pcr, PETXCFG, 0x80, 0x80);
+		rtsx_pci_write_register(pcr, LDO_VCC_CFG0,
+			RTS5261_LDO1_OCP_THD_MASK,
+			pcr->option.sd_800mA_ocp_thd);
+
+		if (pcr->ops->disable_auto_blink)
+			pcr->ops->disable_auto_blink(pcr);
+
+		/* For PCIe/NVMe mode can't enter delink issue */
+		pcr->hw_param.interrupt_en &= ~(SD_INT_EN);
+		rtsx_pci_writel(pcr, RTSX_BIER, pcr->hw_param.interrupt_en);
+
+		rtsx_pci_write_register(pcr, RTS5260_AUTOLOAD_CFG4,
+			RTS5261_AUX_CLK_16M_EN, RTS5261_AUX_CLK_16M_EN);
+		rtsx_pci_write_register(pcr, RTS5261_FW_CFG0,
+			RTS5261_FW_ENTER_EXPRESS, RTS5261_FW_ENTER_EXPRESS);
+		rtsx_pci_write_register(pcr, RTS5261_FW_CFG1,
+			RTS5261_MCU_BUS_SEL_MASK | RTS5261_MCU_CLOCK_SEL_MASK
+			| RTS5261_MCU_CLOCK_GATING | RTS5261_DRIVER_ENABLE_FW,
+			RTS5261_MCU_CLOCK_SEL_16M | RTS5261_MCU_CLOCK_GATING
+			| RTS5261_DRIVER_ENABLE_FW);
+		cmd->error = -EPERM;
+	}
 }
 
 static int sd_read_data(struct realtek_pci_sdmmc *host, struct mmc_command *cmd,
@@ -1123,6 +1162,8 @@ static int sdmmc_get_cd(struct mmc_host *mmc)
 	dev_dbg(sdmmc_dev(host), "%s: RTSX_BIPR = 0x%08x\n", __func__, val);
 	if (val & SD_EXIST)
 		cd = 1;
+	if (pcr->extra_caps & EXTRA_CAPS_SD_EXPRESS)
+		mmc->caps2 |= MMC_CAP2_SD_EXPRESS;
 
 	mutex_unlock(&pcr->pcr_mutex);
 
@@ -1333,6 +1374,8 @@ static void init_extra_caps(struct realtek_pci_sdmmc *host)
 		mmc->caps |= MMC_CAP_1_8V_DDR;
 	if (pcr->extra_caps & EXTRA_CAPS_MMC_8BIT)
 		mmc->caps |= MMC_CAP_8_BIT_DATA;
+	if (pcr->extra_caps & EXTRA_CAPS_SD_EXPRESS)
+		mmc->caps2 |= MMC_CAP2_SD_EXPRESS;
 }
 
 static void realtek_init_host(struct realtek_pci_sdmmc *host)
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index ba703384bea0..7c60998f4b91 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -369,6 +369,7 @@ struct mmc_host {
 #define MMC_CAP2_CQE_DCMD	(1 << 24)	/* CQE can issue a direct command */
 #define MMC_CAP2_AVOID_3_3V	(1 << 25)	/* Host must negotiate down from 3.3V */
 #define MMC_CAP2_MERGE_CAPABLE	(1 << 26)	/* Host can merge a segment over the segment size */
+#define MMC_CAP2_SD_EXPRESS	BIT(27)		/* Host support sd express card */
 
 	int			fixed_drv_type;	/* fixed driver type for non-removable media */
 
diff --git a/include/linux/rtsx_pci.h b/include/linux/rtsx_pci.h
index 65b8142a7fed..a8e1a460645d 100644
--- a/include/linux/rtsx_pci.h
+++ b/include/linux/rtsx_pci.h
@@ -667,6 +667,24 @@
 #define   PM_WAKE_EN			0x01
 #define PM_CTRL4			0xFF47
 
+#define RTS5261_FW_CFG0			0xFF54
+#define   RTS5261_FW_ENTER_EXPRESS	(0x01 << 0)
+
+#define RTS5261_FW_CFG1			0xFF55
+#define   RTS5261_SYS_CLK_SEL_MCU_CLK	(0x01 << 7)
+#define   RTS5261_CRC_CLK_SEL_MCU_CLK	(0x01 << 6)
+#define   RTS5261_FAKE_MCU_CLOCK_GATING	(0x01 << 5)
+#define   RTS5261_MCU_BUS_SEL_MASK	(0x01 << 4)
+#define   RTS5261_MCU_BUS_SEL_MASK	(0x01 << 4)
+#define   RTS5261_MCU_CLOCK_SEL_MASK	(0x03 << 2)
+#define   RTS5261_MCU_CLOCK_SEL_16M	(0x01 << 2)
+#define   RTS5261_MCU_CLOCK_GATING	(0x01 << 1)
+#define   RTS5261_DRIVER_ENABLE_FW	(0x01 << 0)
+#define   RTS5261_MCU_CLOCK_SEL_MASK	(0x03 << 2)
+#define   RTS5261_MCU_CLOCK_SEL_16M	(0x01 << 2)
+#define   RTS5261_MCU_CLOCK_GATING	(0x01 << 1)
+#define   RTS5261_DRIVER_ENABLE_FW	(0x01 << 0)
+
 /* Memory mapping */
 #define SRAM_BASE			0xE600
 #define RBUF_BASE			0xF400
@@ -704,6 +722,12 @@
 /*RTS5260*/
 #define   RTS5260_DVCC_TUNE_MASK	0x70
 #define   RTS5260_DVCC_33		0x70
+/*RTS5261*/
+#define RTS5261_LDO1_CFG0		0xFF72
+#define   RTS5261_LDO1_OCP_THD_MASK	(0x07 << 5)
+#define   RTS5261_LDO1_OCP_EN		(0x01 << 4)
+#define   RTS5261_LDO1_OCP_LMT_THD_MASK	(0x03 << 2)
+#define   RTS5261_LDO1_OCP_LMT_EN	(0x01 << 1)
 
 #define LDO_VCC_CFG1			0xFF73
 #define   LDO_VCC_REF_TUNE_MASK		0x30
@@ -745,6 +769,8 @@
 
 #define RTS5260_AUTOLOAD_CFG4		0xFF7F
 #define   RTS5260_MIMO_DISABLE		0x8A
+/*RTS5261*/
+#define   RTS5261_AUX_CLK_16M_EN		(1 << 5)
 
 #define RTS5260_REG_GPIO_CTL0		0xFC1A
 #define   RTS5260_REG_GPIO_MASK		0x01
@@ -1217,6 +1243,7 @@ struct rtsx_pcr {
 #define EXTRA_CAPS_MMC_HSDDR		(1 << 3)
 #define EXTRA_CAPS_MMC_HS200		(1 << 4)
 #define EXTRA_CAPS_MMC_8BIT		(1 << 5)
+#define EXTRA_CAPS_SD_EXPRESS		(1 << 6)
 	u32				extra_caps;
 
 #define IC_VER_A			0
-- 
2.17.1

Re: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[Greg KH]

On Tue, May 19, 2020 at 03:59:23PM +0800, rui_feng@realsil.com.cn wrote:
> From: rui_feng <rui_feng@realsil.com.cn>
> 
> RTS5261 support legacy SD mode and SD Express mode.
> In SD7.x, SD association introduce SD Express as a new mode.
> SD Express mode is distinguished by CMD8.
> Therefore, CMD8 has new bit for SD Express.
> SD Express is based on PCIe/NVMe.
> RTS5261 uses CMD8 to switch to SD Express mode.
> 
> Signed-off-by: rui_feng <rui_feng@realsil.com.cn>
> ---
> v2: remove config option MISC_RTSX_PCI_SD_EXPRESS 
> ---
> 
>  drivers/misc/cardreader/rts5261.c  |  5 ++++
>  drivers/misc/cardreader/rts5261.h  | 23 ----------------
>  drivers/misc/cardreader/rtsx_pcr.c |  5 ++++
>  drivers/mmc/core/sd_ops.c          |  9 ++++++-
>  drivers/mmc/host/rtsx_pci_sdmmc.c  | 43 ++++++++++++++++++++++++++++++
>  include/linux/mmc/host.h           |  1 +
>  include/linux/rtsx_pci.h           | 27 +++++++++++++++++++
>  7 files changed, 89 insertions(+), 24 deletions(-)

If I can get an ack from the MMC maintainer, I can take this in my
tree...

{hint}

thanks,

greg k-h

Re: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[Arnd Bergmann]

On Fri, May 22, 2020 at 11:16 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, May 19, 2020 at 03:59:23PM +0800, rui_feng@realsil.com.cn wrote:
> > From: rui_feng <rui_feng@realsil.com.cn>
> >
> > RTS5261 support legacy SD mode and SD Express mode.
> > In SD7.x, SD association introduce SD Express as a new mode.
> > SD Express mode is distinguished by CMD8.
> > Therefore, CMD8 has new bit for SD Express.
> > SD Express is based on PCIe/NVMe.
> > RTS5261 uses CMD8 to switch to SD Express mode.
> >
> > Signed-off-by: rui_feng <rui_feng@realsil.com.cn>
> > ---
> > v2: remove config option MISC_RTSX_PCI_SD_EXPRESS
> > ---
> >
> >  drivers/misc/cardreader/rts5261.c  |  5 ++++
> >  drivers/misc/cardreader/rts5261.h  | 23 ----------------
> >  drivers/misc/cardreader/rtsx_pcr.c |  5 ++++
> >  drivers/mmc/core/sd_ops.c          |  9 ++++++-
> >  drivers/mmc/host/rtsx_pci_sdmmc.c  | 43 ++++++++++++++++++++++++++++++
> >  include/linux/mmc/host.h           |  1 +
> >  include/linux/rtsx_pci.h           | 27 +++++++++++++++++++
> >  7 files changed, 89 insertions(+), 24 deletions(-)
>
> If I can get an ack from the MMC maintainer, I can take this in my
> tree...
>
> {hint}

I think this feature needs much more discussion to make sure we
get a good user experience when it gets added to all mmc controllers.

rtsx is a bit of a special case for mmc controllers already, but we will
likely see the same requirements for a lot more mmc host drivers.

I suspect we need to tie in both the mmc block and nvme device
drivers to properly do a handover, to ensure that there is a way to
identify the block device as reliably getting probed as at least one
of the two (sd or nvme) and to get identified as the same device
during the handover, in particular across a suspend or hibernate
event.

I understand that this patch is very desirable for users, but let's
not rush it.

     Arnd

答复: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[冯锐]

> On Fri, May 22, 2020 at 11:16 AM Greg KH <gregkh@linuxfoundation.org>
> wrote:
> >
> > On Tue, May 19, 2020 at 03:59:23PM +0800, rui_feng@realsil.com.cn wrote:
> > > From: rui_feng <rui_feng@realsil.com.cn>
> > >
> > > RTS5261 support legacy SD mode and SD Express mode.
> > > In SD7.x, SD association introduce SD Express as a new mode.
> > > SD Express mode is distinguished by CMD8.
> > > Therefore, CMD8 has new bit for SD Express.
> > > SD Express is based on PCIe/NVMe.
> > > RTS5261 uses CMD8 to switch to SD Express mode.
> > >
> > > Signed-off-by: rui_feng <rui_feng@realsil.com.cn>
> > > ---
> > > v2: remove config option MISC_RTSX_PCI_SD_EXPRESS
> > > ---
> > >
> > >  drivers/misc/cardreader/rts5261.c  |  5 ++++
> > > drivers/misc/cardreader/rts5261.h  | 23 ----------------
> > > drivers/misc/cardreader/rtsx_pcr.c |  5 ++++
> > >  drivers/mmc/core/sd_ops.c          |  9 ++++++-
> > >  drivers/mmc/host/rtsx_pci_sdmmc.c  | 43
> ++++++++++++++++++++++++++++++
> > >  include/linux/mmc/host.h           |  1 +
> > >  include/linux/rtsx_pci.h           | 27 +++++++++++++++++++
> > >  7 files changed, 89 insertions(+), 24 deletions(-)
> >
> > If I can get an ack from the MMC maintainer, I can take this in my
> > tree...
> >
> > {hint}
> 
> I think this feature needs much more discussion to make sure we get a good
> user experience when it gets added to all mmc controllers.
> 
Only RTS5261 is affected by this patch. Other vendor's reader won't be affected.

> rtsx is a bit of a special case for mmc controllers already, but we will likely see
> the same requirements for a lot more mmc host drivers.
> 
The modification in mmc core in this patch is according to chapter 4.3.13 in the spec "Physical Layer Simplified Specification Version 7.10" released by SD Association,
anyone can get it on https://www.sdcard.org/downloads/pls/index.html. Any other vendor which want to support SD7.x must obey the spec.

> I suspect we need to tie in both the mmc block and nvme device drivers to
> properly do a handover, to ensure that there is a way to identify the block
> device as reliably getting probed as at least one of the two (sd or nvme) and to
> get identified as the same device during the handover, in particular across a
> suspend or hibernate event.
> 
Our card reader will be tested by ODM/OEM before used by end users.

Kind regards

Re: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[Arnd Bergmann]

On Mon, May 25, 2020 at 8:58 AM 冯锐 <rui_feng@realsil.com.cn> wrote:
> > On Fri, May 22, 2020 at 11:16 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > If I can get an ack from the MMC maintainer, I can take this in my
> > > tree...
> > >
> > > {hint}
> >
> > I think this feature needs much more discussion to make sure we get a good
> > user experience when it gets added to all mmc controllers.
> >
> Only RTS5261 is affected by this patch. Other vendor's reader won't be affected.

That sounds like another problem with this patch:

The transition should probably be handled by the MMC core checking whether
the kernel, the mmc host and and the card all support SD express mode, and
then start the transition as well as falling back to SD mode if it doesn't come
up properly.

         Arnd

答复: [PATCH] [V2] mmc: rtsx: Add SD Express mode support for RTS5261

[冯锐]

> On Mon, May 25, 2020 at 8:58 AM 冯锐 <rui_feng@realsil.com.cn> wrote:
> > > On Fri, May 22, 2020 at 11:16 AM Greg KH <gregkh@linuxfoundation.org>
> wrote:
> > > >
> > > > If I can get an ack from the MMC maintainer, I can take this in my
> > > > tree...
> > > >
> > > > {hint}
> > >
> > > I think this feature needs much more discussion to make sure we get
> > > a good user experience when it gets added to all mmc controllers.
> > >
> > Only RTS5261 is affected by this patch. Other vendor's reader won't be
> affected.
> 
> That sounds like another problem with this patch:
> 
> The transition should probably be handled by the MMC core checking whether
> the kernel, the mmc host and and the card all support SD express mode, and
> then start the transition as well as falling back to SD mode if it doesn't come up
> properly.
> 
The purpose of the modification in mmc core of this patch is to let the kernel has the ability
to check whether the card support SD express mode according to SD specification.
If RTS5261 switch to SD express mode failed, RTS5261 will fall back to SD mode by itself
and It doesn't need mmc driver to do anything. After falling back to SD mode, mmc driver
will handle the SD card in SD mode as before without this patch.

Kind regards