[PATCH v5 2/2] mmc: core: Honor keep-power-in-suspend for (e)MMC in suspend/resume

On some platforms, firmware accesses the (e)MMC card directly during
resume from Suspend-to-DRAM, before the kernel's own resume path has
run, in order to load boot code. This requires the card to remain
powered and responsive throughout suspend: putting it to sleep,
sending it a power-off notification, or removing its supply is not
safe, since firmware needs to talk to a live card.

keep-power-in-suspend / MMC_PM_KEEP_POWER already exist for this
purpose, but are only consumed in the SDIO suspend/resume path
(mmc_sdio_suspend()/mmc_sdio_resume()), gated on a per-function
runtime request via sdio_set_host_pm_flags(). (e)MMC has no
equivalent function-driver layer to make that request, and the
requirement here is a fixed platform characteristic rather than a
per-cycle one, so _mmc_suspend() checks host->pm_caps directly
instead of pm_flags.

When pm_caps has MMC_PM_KEEP_POWER set and pm_type is
MMC_POWEROFF_SUSPEND, skip the poweroff-notify/sleep/power-off
sequence entirely: deselect the card, reset the host to its initial
bus state the same way _mmc_hw_reset() does for a non-power-cycle
reset, mark the card suspended, and set host->pm_flags |=
MMC_PM_KEEP_POWER.

Setting MMC_PM_KEEP_POWER in host->pm_flags during suspend ensures
that host controller resume handlers are aware that card power was
preserved across suspend, allowing them to perform a soft resume
sequence instead of assuming power was lost. Clear this flag in
_mmc_resume() upon completion.

Only set pm_flags and mark the card suspended after
mmc_deselect_cards() succeeds. If it fails, the card is never marked
suspended, so _mmc_resume() takes its early "not suspended" exit and
never reaches the code that clears MMC_PM_KEEP_POWER -- setting the
flag unconditionally would leak it for the remainder of uptime.

The pm_type check matters because _mmc_suspend() is also called for
shutdown, driver unbind, and undervoltage, none of which are
guaranteed a subsequent _mmc_resume() call, so those still need the
normal power-off path.

Reported-by: Florian Fainelli <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Kamal Dasu <[email protected]>
---
Changes in v5:
  - Only set host->pm_flags |= MMC_PM_KEEP_POWER after
    mmc_deselect_cards() succeeds, instead of unconditionally before
    it. Otherwise, if the deselect fails, the card is never marked
    suspended, _mmc_resume() takes its early exit, and the flag never
    gets cleared -- leaking it for the rest of uptime.

Changes in v4:
  - Gated the fast path on pm_type == MMC_POWEROFF_SUSPEND; it was
    previously unconditional, so it wrongly skipped the required
    power-off/notify handling during shutdown, unbind and
    undervoltage as well.
  - Reset the host to its initial bus state (mmc_set_clock() +
    mmc_set_initial_state(), matching _mmc_hw_reset()'s non-power-
    cycle path) before marking the card suspended.
  - Set/clear host->pm_flags |= MMC_PM_KEEP_POWER around the suspend/
    resume, mirroring the SDIO convention, so host controller resume
    handlers can tell power was preserved and perform a soft resume
    sequence instead of assuming power was lost.
  - Dropped MMC_CAP2_NO_POWEROFF_SUSPEND and the no-mmc-poweroff-
    suspend DT property entirely. Reuse keep-power-in-suspend /
    MMC_PM_KEEP_POWER instead, per Krzysztof's point that the new
    property described the same contract as the existing one.
    _mmc_suspend() now checks host->pm_caps directly rather than
    pm_flags, since (e)MMC has no per-function driver to make the
    dynamic sdio_set_host_pm_flags()-style request SDIO uses.

Changes in v3:
  - Reworked _mmc_suspend() to skip poweroff-notify/sleep/power-off
    entirely, not just SLEEP, per Ulf.
  - Renamed to MMC_CAP2_NO_POWEROFF_SUSPEND/no-mmc-poweroff-suspend.

Changes in v2:
  - Replaced the card-level MMC_QUIRK_BROKEN_SLEEP quirk with a host
    capability, per Ulf.
  - Added Reported-by/Closes crediting Florian.

 drivers/mmc/core/mmc.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 05444ecf3909..7cbe65532726 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -2157,6 +2157,35 @@ static int _mmc_suspend(struct mmc_host *host, enum mmc_poweroff_type pm_type)
 			goto out;
 	}
 
+	/*
+	 * Keep the card powered across an actual suspend; shutdown, unbind
+	 * and undervoltage still need the normal power-off path below,
+	 * since they aren't guaranteed a subsequent _mmc_resume().
+	 *
+	 * Check pm_caps, not pm_flags: unlike SDIO, (e)MMC has no
+	 * per-function driver to request this via
+	 * sdio_set_host_pm_flags(), so it's a fixed platform trait here.
+	 *
+	 * Set MMC_PM_KEEP_POWER in pm_flags so host controller drivers
+	 * know card power was preserved during suspend and perform a
+	 * soft resume sequence.
+	 *
+	 * Reset the host to its initial bus state like _mmc_hw_reset()
+	 * does.
+	 */
+	if (pm_type == MMC_POWEROFF_SUSPEND &&
+	    (host->pm_caps & MMC_PM_KEEP_POWER)) {
+		if (!mmc_host_is_spi(host))
+			err = mmc_deselect_cards(host);
+		if (!err) {
+			host->pm_flags |= MMC_PM_KEEP_POWER;
+			mmc_set_clock(host, host->f_init);
+			mmc_set_initial_state(host);
+			mmc_card_set_suspended(host->card);
+		}
+		goto out;
+	}
+
 	if (mmc_card_can_poweroff_notify(host->card) &&
 	    mmc_host_can_poweroff_notify(host, pm_type))
 		err = mmc_poweroff_notify(host->card, notify_type);
@@ -2220,6 +2249,7 @@ static int _mmc_resume(struct mmc_host *host)
 	mmc_power_up(host, host->card->ocr);
 	err = mmc_init_card(host, host->card->ocr, host->card);
 	mmc_card_clr_suspended(host->card);
+	host->pm_flags &= ~MMC_PM_KEEP_POWER;
 
 out:
 	mmc_release_host(host);
-- 
2.34.1