[PATCH v2 0/2] mmc: core: Add a host capability to skip SLEEP for cards with a broken resume

This is v2 of Florian's original patch:

  Link: https://lore.kernel.org/r/[email protected]/

Background: the Kioxia 016G01 eMMC takes ~10ms to exit SLEEP (CMD5)
instead of the ~1ms it advertises via S_A_TIMEOUT, which can be
problematic on systems that resume from Suspend-to-DRAM by first
pulling boot code from eMMC using hard wired logic that is not field
updatable -- if the card is still asleep when that logic reads it, it
resets the board. The device stays powered throughout suspend-to-
DRAM (no software-controlled VCC/VCCQ regulator toggling on this
path), and the CMD0-before-resume sequence follows the JEDEC boot
spec, so this isn't something the kernel's resume ordering can fix
on its own.

v1 addressed this with a card-level MMC_QUIRK_BROKEN_SLEEP quirk
keyed off the device CID. Ulf pointed out that a device-specific
quirk doesn't generalize well and suggested a host capability bit
instead, settable from DT (or derived from a compatible string),
mirroring the existing no-sdio/no-sd/no-mmc properties. Oleksij
separately noted that quirks registered in mmc_blk_fixups[] are only
applied once the mmc_block driver probes, which is too late to avoid
a race against an earlier SLEEP/poweroff triggered on an under-
voltage path -- a host cap resolved in mmc_of_parse(), before any
card exists, sidesteps that ordering problem entirely.

This series implements that direction:

  - Patch 1 documents a new "no-mmc-sleep" DT flag property.
  - Patch 2 adds MMC_CAP2_NO_SLEEP_CMD, parses the DT property in
    mmc_of_parse(), and has mmc_card_can_sleep() honor it.

The actual board DT change (adding "no-mmc-sleep;" to the affected
brcmstb eMMC controller node) will follow separately once this lands,
since that DT lives outside of mainline.

Changes in v2:
  - Dropped the card-quirk/CID-match approach entirely in favor of a
    host capability bit, per Ulf's suggestion.
  - Added a DT property ("no-mmc-sleep") to set that capability,
    following the no-sdio/no-sd/no-mmc precedent, per Ulf.
  - This also resolves Oleksij's concern about mmc_blk_fixups[]
    being applied too late to close the race on an early
    SLEEP/poweroff path, since the host cap is resolved in
    mmc_of_parse() before a card exists.
  - Reworded the rationale in patch 1's commit message and binding
    description per Florian's review.
  - Added a Reported-by/Closes tag crediting Florian for the
    original bug report.

Kamal Dasu (2):
  dt-bindings: mmc: Document no-mmc-sleep property
  mmc: core: Add MMC_CAP2_NO_SLEEP_CMD host capability

 .../devicetree/bindings/mmc/mmc-controller-common.yaml    | 8 ++++++++
 drivers/mmc/core/host.c                                   | 2 ++
 drivers/mmc/core/mmc.c                                    | 3 +++
 include/linux/mmc/host.h                                  | 1 +
 4 files changed, 14 insertions(+)

-- 
2.34.1