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drivers/mmcsd: fix eMMC bus width switch sequencing

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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 <thirteenking.wang@gmail.com>
This commit is contained in:
DuoYuWang 2026-07-22 11:56:31 +08:00 • committed by Xiang Xiao
parent 6bd674b4e4
commit e84259cbcc
1 changed files with 25 additions and 1 deletions
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26
drivers/mmcsd/mmcsd_sdio.c
View file

@ -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.
*/