From: Peng Fan <[email protected]>
Commit 906ee6785b1c ("mmc: sd: Handle UHS-I voltage signaling without
power cycle") added detection of cards already operating at 1.8V
signaling via mmc_sd_card_using_v18(). This correctly handles the
warm-reboot scenario in mmc_startup().
However, mmc_deinit() strips ALL UHS capabilities from the card caps
and calls sd_select_mode_and_width() to downgrade the card before
kernel handoff. For a card that has switched to 1.8V, uhs_en is
already true (via OCR_S18R in mmc->ocr), so sd_select_mode_and_width()
attempts UHS mode selection -- but no UHS modes remain in the filtered
caps. The non-UHS fallbacks (SD_HS, MMC_LEGACY) are 3.3V speed modes
which, when selected while signaling at 1.8V, leave the card in an
inconsistent state it cannot recover from without a power cycle.
Per SD Physical Layer Specification: "Once the card enters 1.8V
signaling mode, the card cannot be switched to 3.3V signaling without
power cycle. If the card receives CMD0, card returns to Idle state but
still works with SDR12 timing."
Fix by using a UHS capability mask that preserves UHS_SDR12 when the
card is operating at 1.8V. SDR12 is the minimum valid UHS-I mode and
is always available at 1.8V signaling per the SD specification, so the
card is left in a consistent (1.8V) state at a low, safe speed.
Fixes: 906ee6785b1c ("mmc: sd: Handle UHS-I voltage signaling without power
cycle")
Signed-off-by: Peng Fan <[email protected]>
---
drivers/mmc/mmc.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 5fd12d21f92..135fd835609 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -3173,10 +3173,19 @@ int mmc_deinit(struct mmc *mmc)
return 0;
if (IS_SD(mmc)) {
- caps_filtered = mmc->card_caps &
- ~(MMC_CAP(UHS_SDR12) | MMC_CAP(UHS_SDR25) |
- MMC_CAP(UHS_SDR50) | MMC_CAP(UHS_DDR50) |
- MMC_CAP(UHS_SDR104));
+ u32 uhs_mask = UHS_CAPS;
+
+#if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
+ /*
+ * Per SD spec, once a card enters 1.8V signaling it
+ * cannot revert to 3.3V without a power cycle.
+ * If the card is operating at 1.8V, keep UHS_SDR12
+ * as the minimum fallback mode.
+ */
+ if (mmc_sd_card_using_v18(mmc))
+ uhs_mask &= ~MMC_CAP(UHS_SDR12);
+#endif
+ caps_filtered = mmc->card_caps & ~uhs_mask;
return sd_select_mode_and_width(mmc, caps_filtered);
} else {
--
2.51.0
