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The following commit(s) were added to refs/heads/master by this push:
new e84259cbcc3 drivers/mmcsd: fix eMMC bus width switch sequencing
e84259cbcc3 is described below
commit e84259cbcc33cc6cc98abe11caac2f34413a62bf
Author: DuoYuWang <[email protected]>
AuthorDate: Wed Jul 22 11:56:31 2026 +0800
drivers/mmcsd: fix eMMC bus width switch sequencing
Two sequencing problems in the MMC wide bus path break eMMC 4-bit
operation on hosts that program the bus width in the SDIO widebus /
clock callbacks (e.g. STM32H7):
1. The SWITCH command (CMD6) is issued before the host has switched
to wide bus operation. When the card completes the switch while
the host is still in 1-bit mode the switch never takes effect and
every following data transfer times out. Switch the host to wide
bus operation before issuing CMD6.
2. The transfer clock is selected only at the end of mmcsd_widebus(),
so the whole switch sequence runs at ID-mode clock and, on the
affected hosts, the final clock update does not take effect either,
leaving the bus at ~400 kHz. Select the MMC transfer clock before
calling mmcsd_widebus(), and pick CLOCK_MMC_TRANSFER_4BIT when wide
bus operation is active (mirroring the SD card path) so a later
clock selection cannot revert the host to 1-bit.
No behavior change for SD cards, and no change on hosts whose widebus
callback only records the requested state.
Tested on a custom STM32H743 board with eMMC: sd_bench sequential
write ~4.1 MB/s, sequential read ~6.3 MB/s (previously all data
transfers timed out).
Signed-off-by: DuoYuWang <[email protected]>
---
drivers/mmcsd/mmcsd_sdio.c | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/drivers/mmcsd/mmcsd_sdio.c b/drivers/mmcsd/mmcsd_sdio.c
index c034f48fef5..f81412704d4 100644
--- a/drivers/mmcsd/mmcsd_sdio.c
+++ b/drivers/mmcsd/mmcsd_sdio.c
@@ -2848,8 +2848,17 @@ static int mmcsd_widebus(FAR struct mmcsd_state_s *priv)
{
/* Configuring MMC - Use MMC_SWITCH access modes.
* Select 8-bit if host supports it, otherwise 4-bit.
+ *
+ * Switch the host to wide bus operation before issuing the
+ * SWITCH command: on hosts that program the bus width in the
+ * widebus callback, switching the card first leaves the switch
+ * unfinished and all following transfers fail.
*/
+ SDIO_WIDEBUS(priv->dev, true);
+ priv->widebus = true;
+ MMCSD_USLEEP(MMCSD_CLK_DELAY);
+
if (priv->caps & SDIO_CAPS_8BIT)
{
mmcsd_sendcmdpoll(priv, MMCSD_CMD6,
@@ -2936,7 +2945,13 @@ static int mmcsd_widebus(FAR struct mmcsd_state_s *priv)
priv->mode = EXT_CSD_HS_TIMING_HS;
}
- SDIO_CLOCK(priv->dev, CLOCK_MMC_TRANSFER);
+ /* Select the MMC transfer clocking according to the negotiated
+ * bus width, mirroring the SD card path above, so that a later
+ * clock selection cannot revert the host to 1-bit operation.
+ */
+
+ SDIO_CLOCK(priv->dev, priv->widebus ? CLOCK_MMC_TRANSFER_4BIT :
+ CLOCK_MMC_TRANSFER);
}
#endif /* #ifdef CONFIG_MMCSD_MMCSUPPORT */
@@ -3171,6 +3186,15 @@ static int mmcsd_mmcinitialize(FAR struct mmcsd_state_s
*priv)
mmcsd_decode_csd(priv, priv->csd);
+ /* Select high speed MMC clocking (which may depend on the DSR setting)
+ * before switching the bus width: on hosts that program the bus width
+ * in the clock callback, the transfer clock must already be in place
+ * before the switch sequence starts.
+ */
+
+ SDIO_CLOCK(priv->dev, CLOCK_MMC_TRANSFER);
+ MMCSD_USLEEP(MMCSD_CLK_DELAY);
+
/* It's up to the driver to act on the widebus request. mmcsd_widebus()
* enables the CLOCK_MMC_TRANSFER, so call it here always.
*/
