[PATCH 1/2] mmc: core: sdio: retry without UHS if UHS init fails

[Deomid rojer Ryabkov <rojer@rojer.me>]

If mmc_sdio_init_uhs_card() fails, typically because tuning finds no
working sample phase, card initialisation fails and the card is not
usable at all, even though it would work fine in high-speed mode.

This happens for example on the FriendlyElec NanoPi R2S Plus when the
SDIO pins of the RTL8822CS Wi-Fi module are left at their default 4 mA
drive strength:

  dwmmc_rockchip ff5f0000.mmc: All phases bad!
  mmc2: tuning execution failed: -5
  mmc2: error -5 whilst initialising SDIO card
  [... repeated for every init frequency ...]
  mmc2: Failed to initialize a non-removable card

There is already a fallback for a failure to read the CCCR in UHS mode:
power-cycle the card and restart the init sequence without
R4_18V_PRESENT. Do the same when UHS init fails, so that the card comes
up in high-speed mode instead:

  mmc2: UHS init failed (-5), retrying without UHS
  mmc2: Skipping voltage switch
  mmc2: new high speed SDIO card at address 0001

The fallback is taken at most once, as the retry doesn't request UHS.

Signed-off-by: Deomid rojer Ryabkov <rojer@rojer.me>
---
 drivers/mmc/core/sdio.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
index 83085e7648..6787fdf1c5 100644
--- a/drivers/mmc/core/sdio.c
+++ b/drivers/mmc/core/sdio.c
@@ -867,8 +867,14 @@ static int mmc_sdio_init_card(struct mmc_host *host, u32 ocr,
 	/* Only if card supports 1.8v and UHS signaling */
 	if ((ocr & R4_18V_PRESENT) && card->sw_caps.sd3_bus_mode) {
 		err = mmc_sdio_init_uhs_card(card);
-		if (err)
-			goto remove;
+		if (err) {
+			pr_warn("%s: UHS init failed (%d), retrying without UHS\n",
+				mmc_hostname(host), err);
+			mmc_sdio_pre_init(host, ocr_card,
+					  card != oldcard ? card : NULL);
+			retries = 0;
+			goto try_again;
+		}
 	} else {
 		/*
 		 * Switch to high-speed (if supported).
-- 
2.53.0