[PATCH v3 0/4] mmc: sdhci_am654: Fix DDR50 mode for cards without tuning support

[Diogo Ivo (Schneider Electric)]

DDR50 mode is not required to support the tuning command CMD19 by the
eMMC/SD specification, meaning that calibration may fail on cards that
do not implement it. This series fixes four issues discovered when
using such cards:

  - Patch 1 moves the tuning_loop counter from a persistent struct field
    to a local variable, preventing failed tuning attempts from depleting
    the retry budget across calls.

  - Patch 2 ensures the command/data line reset is always performed
    after tuning, even on failure, preventing stale data in the
    controller buffer.

  - Patch 3 clears the ITAPDLY enable and delay values on tuning
    failure so that leftover calibration values do not interfere with
    subsequent I/O.

  - Patch 4 falls back to the DT-provided itap delay value for DDR50
    when tuning fails in this mode, making a best-effort attempt at a
    known-good delay being programmed.

Together these changes make DDR50 functional on TI J721E SoCs with
cards that lack CMD19 tuning support. This second version addresses
all comments from Sashiko, which I found to be correct.

Signed-off-by: Diogo Ivo (Schneider Electric) <diogo.ivo@xxxxxxxxxxx>
---
Changes in v3:
- Collect R-b from Judith and A-b from Adrian
- Add debug print when applying DT fallback values (Patch 4)
- Link to v2: https://patch.msgid.link/20260803-am654-sdhci-v2-0-a5ee5be86133@xxxxxxxxxxx

Changes in v2:
- Add new patch moving tuning_loop to a local variable (Patch 1)
- Clear ITAPDLY array values alongside HW registers on tuning failure (Patch 3)
- Save DT-provided itap delay values for DDR50 in dedicated variables
  to preserve them across tuning cycles (Patch 4)
- Link to v1: https://patch.msgid.link/20260729-am654-sdhci-v1-0-7568108e4b9a@xxxxxxxxxxx

---
Diogo Ivo (Schneider Electric) (4):
      mmc: sdhci_am654: Move tuning_loop to local variable
      mmc: sdhci_am654: Reset command and data lines on failed tuning
      mmc: sdhci_am654: Clear ITAPDLY on tuning failure
      mmc: sdhci_am654: Fallback to DT-provided itap delay on DDR50 tuning failure

 drivers/mmc/host/sdhci_am654.c | 43 +++++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 15 deletions(-)
---
base-commit: f9a2394a23482bfd330911e9c8295b71724feacd
change-id: 20260728-am654-sdhci-85094d458bae

Best regards,
--  
Diogo Ivo <diogo.ivo@xxxxxxxxxxx>