Re: [PATCH v4] mmc: litex_mmc: Set mandatory idle clocks before CMD0

[Inochi Amaoto]

On Mon, May 18, 2026 at 06:45:26PM -0400, Gabriel L. Somlo wrote:
> On Tue, May 19, 2026 at 06:24:19AM +0800, Inochi Amaoto wrote:
> > On Mon, May 18, 2026 at 06:20:49PM -0400, Gabriel L. Somlo wrote:
> > > with this patch on top of today's latest (4d3a2a466b8d), I get
> > > (on 64-bit rocketchip with Litex):
> > > 
> > > [    6.475114] mmc0: invalid bus width
> > > [    6.477870] mmc0: error -22 whilst initialising SD card
> > > 
> > > Thanks,
> > > --Gabriel
> > > 
> > 
> > Hi, Gabriel,
> > 
> > Could you share the board link and build commands? I think I need to
> > take a look for why this occurs.
> > 
> > Regards,
> > Inochi
> 
> Hi Inochi,
> 
> it's the digilent nexys-video board; the command line to build the
> bitstream is:
> 
> litex-boards/litex_boards/targets/digilent_nexys_video.py --build \
>   --cpu-type rocket --cpu-variant linux --cpu-num-cores 4 --cpu-mem-width 2 \
>   --sys-clk-freq 50e6 --with-ethernet --with-sdcard --with-sata --sata-gen 1
> 
> (for more details see https://github.com/litex-hub/linux-on-litex-rocket)
> 
> I've added your patch on top of the LiteX kernel tree at
> https://github.com/litex-hub/linux/tree/litex-rebase
> 
> and compiled it with:
> 
> make clean
> make ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu- litex_rocket_defconfig
> make ARCH=riscv CROSS_COMPILE=riscv64-unknown-linux-gnu-
> 
> FWIW, your previous versions of the patch did work, and did fix the
> issue you were trying to address (which I did notice being a problem
> on my configuration :)
> 
> Thanks,
> --Gabriel
>  

Hi Gabriel,

Although I fail to compile the rocket and can not reproduced this
error with VexiiRiscv, I have noticed some interesting things:

[  745.321341] mmc0: card aaaa removed
[  745.363624] litex-mmc f0004000.mmc: clock 25000000 -> 0
[  747.357770] litex-mmc f0004000.mmc: clock 0 -> 12500000
[  747.374898] litex-mmc f0004000.mmc: clock 12500000 -> 400000
[  747.706917] litex-mmc f0004000.mmc: clock 400000 -> 25000000
[  747.711954] mmc0: new SDHC card at address aaaa
[  747.722665] mmcblk0: mmc0:aaaa SL16G 14.8 GiB
[  747.751452]  mmcblk0: p1 p2

It seems like that the controller does not switch to the required init
frequency. Instead, it jump to a working frequency. It may lead to a
false reset.

Another thing is that I noticed the bios sets the PHY to x1 when
initing, but the current set_ios() does nothing with this, only
setting x4 every time that sends the command. I have added a simple
reset that changes the PHY to x1 when setting MMC_CS_HIGH.
(And I think it could be better to add bus width length handler
instead of leaving a force x4 mode).

I have prepared a new patch for these thing. Could you have a try?

Regards,
Inochi

diff --git a/drivers/mmc/host/litex_mmc.c b/drivers/mmc/host/litex_mmc.c
index d2f19c2dc673..97e07222872e 100644
--- a/drivers/mmc/host/litex_mmc.c
+++ b/drivers/mmc/host/litex_mmc.c
@@ -28,6 +28,7 @@
 #define LITEX_PHY_CLOCKERDIV  0x04
 #define LITEX_PHY_INITIALIZE  0x08
 #define LITEX_PHY_WRITESTATUS 0x0C
+#define LITEX_PHY_SETTINGS    0x18
 #define LITEX_CORE_CMDARG     0x00
 #define LITEX_CORE_CMDCMD     0x04
 #define LITEX_CORE_CMDSND     0x08
@@ -68,6 +69,12 @@
 #define SD_SLEEP_US       5
 #define SD_TIMEOUT_US 20000
 
+#define SD_INIT_DELAY_US  1000
+#define SD_INIT_CLK_HZ    400000
+
+#define SD_PHY_SPEED_1X 0
+#define SD_PHY_SPEED_4X 1
+
 #define SDIRQ_CARD_DETECT    1
 #define SDIRQ_SD_TO_MEM_DONE 2
 #define SDIRQ_MEM_TO_SD_DONE 4
@@ -220,6 +227,8 @@ static int litex_mmc_set_bus_width(struct litex_mmc_host *host)
 	if (ret)
 		return ret;
 
+	litex_write8(host->sdphy + LITEX_PHY_SETTINGS, SD_PHY_SPEED_4X);
+
 	/* Re-send 'app_cmd' if necessary */
 	if (app_cmd_sent) {
 		ret = litex_mmc_send_app_cmd(host);
@@ -449,6 +458,12 @@ static void litex_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 {
 	struct litex_mmc_host *host = mmc_priv(mmc);
 
+	if (ios->chip_select == MMC_CS_HIGH) {
+		litex_write8(host->sdphy + LITEX_PHY_SETTINGS, SD_PHY_SPEED_1X);
+		ios->clock = SD_INIT_CLK_HZ;
+		host->is_bus_width_set = false;
+	}
+
 	/*
 	 * NOTE: Ignore any ios->bus_width updates; they occur right after
 	 * the mmc core sends its own acmd6 bus-width change notification,
@@ -457,8 +472,14 @@ static void litex_mmc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 	 */
 
 	/* Update sd_clk */
-	if (ios->clock != host->sd_clk)
+	if (ios->clock != host->sd_clk) {
 		litex_mmc_setclk(host, ios->clock);
+	}
+
+	if (ios->chip_select == MMC_CS_HIGH) {
+		litex_write8(host->sdphy + LITEX_PHY_INITIALIZE, 1);
+		fsleep(SD_INIT_DELAY_US);
+	}
 }
 
 static const struct mmc_host_ops litex_mmc_ops = {
@@ -590,7 +611,7 @@ static int litex_mmc_probe(struct platform_device *pdev)
 	 * Set default sd_clk frequency range based on empirical observations
 	 * of LiteSDCard gateware behavior on typical SDCard media
 	 */
-	mmc->f_min = 12.5e6;
+	mmc->f_min = SD_INIT_CLK_HZ;
 	mmc->f_max = 50e6;
 
 	ret = mmc_of_parse(mmc);
---