mmc: avoid removing non-removable hosts during suspend

The Weibu F3C MiniPC has an onboard AP6255 module, presenting
two SDIO functions on a single MMC host (Bluetooth/btsdio and
WiFi/brcmfmac), and the mmc layer correctly detects this as
non-removable.

After suspend/resume, the wifi and bluetooth interfaces disappear
and do not get probed again.

The conditions here are:

 1. During suspend, we reach mmc_pm_notify()

 2. mmc_pm_notify() calls mmc_sdio_pre_suspend() to see if we can
    suspend the SDIO host. However, mmc_sdio_pre_suspend() returns
    -ENOSYS because btsdio_driver does not have a suspend method.

 3. mmc_pm_notify() proceeds to remove the card

 4. Upon resume, mmc_rescan() does nothing with this host, because of
    the rescan_entered check which aims to only scan a non-removable
    device a single time (i.e. during boot).

Fix the loss of functionality by detecting that we are unable to
suspend a non-removable host, so avoid the forced removal in that
case. The comment above this function already indicates that this
code was only intended for removable devices.

Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/core.c

@@ -2761,6 +2761,14 @@ static int mmc_pm_notify(struct notifier_block *notify_block,
 		if (!err)
 			break;
 
+		if (!mmc_card_is_removable(host)) {
+			dev_warn(mmc_dev(host),
+				 "pre_suspend failed for non-removable host: "
+				 "%d\n", err);
+			/* Avoid removing non-removable hosts */
+			break;
+		}
+
 		/* Calling bus_ops->remove() with a claimed host can deadlock */
 		host->bus_ops->remove(host);
 		mmc_claim_host(host);