[PATCH 2/2 alt] mmc: core: sdio: retry without CMD11 if it fails at 1.8V

[Deomid rojer Ryabkov]

Per the SDIO Simplified Specification Version 3.00, section 3.1.2, a card
whose signalling is already at 1.8V must report S18A = 0 in the R4
response, and the core relies on that: it only sends CMD11
(SD_SWITCH_VOLTAGE) when S18A is set.

Some cards don't follow this. The Realtek RTL8822CS (as fitted on the
FriendlyElec NanoPi R2S Plus, where the M.2 SDIO bus is wired to a fixed
1.8V vqmmc) answers CMD5 with S18A = 1 even though the bus is already at
1.8V. CMD11 then times out, the core drops R4_18V_PRESENT and the card
ends up in 50 MHz high-speed mode instead of SDR104.

Keep sending CMD11 as before, but if it fails and the signalling is
still at 1.8V after the power cycle (i.e. vqmmc can't do 3.3V), there was
nothing to switch: power-cycle and retry init once without CMD11, keeping
R4_18V_PRESENT so that UHS init runs:

  dwmmc_rockchip ff5f0000.mmc: Unexpected CMD11 timeout
  mmc_host mmc2: Timeout sending command (cmd 0x10202000 arg 0x0 status 0x90202000)
  mmc2: CMD11 failed at 1.8V, retrying without it
  dwmmc_rockchip ff5f0000.mmc: Successfully tuned phase to 66
  mmc2: new ultra high speed SDR104 SDIO card at address 0001

Cards that handle CMD11 today, compliant or not, are not affected, nor
are hosts that can switch to 3.3V, as they are back at 3.3V after the
power cycle. The cost is the failed CMD11 on affected boards: on the
R2S Plus the card comes up about 0.85s later than when CMD11 is skipped
outright (1.65-1.71s vs. 0.82-0.83s after boot).

FriendlyElec's BSP for this board works around this with a card
quirk, MMC_QUIRK_BROKEN_ROCR_S18A[1], matched on the "realtek,rtl8822cs"
compatible, which drops the switch request whenever this chip is
present. The misreported S18A is the card's fault, but ignoring it is
only correct when the bus is already at 1.8V: on a board with a
switchable vqmmc the same chip would then be run in UHS at 3.3V. A card
quirk would need knowledge of the board's supply that it doesn't have.
The core can tell from a failed CMD11 at 1.8V that there was nothing to
switch, so handle it there, which also takes care of any other card that
turns out to behave the same way.

[1] https://github.com/friendlyarm/kernel-rockchip/commit/aee62cf7ae16b5ede6c6d92a8ee20e796482754e
Cc: Jensen Huang <jensenhuang@xxxxxxxxxxxxxxx>
Signed-off-by: Deomid rojer Ryabkov <rojer@xxxxxxxx>
---
This is an alternative to patch 2/2 ("mmc: core: sdio: skip CMD11 if
signalling is already 1.8V"); apply one or the other. 2/2 follows the
spec and skips CMD11; this one keeps sending it and only retries without
it if it fails at 1.8V, at the cost of ~0.85s on affected boards.

 drivers/mmc/core/sdio.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
index 6787fdf1c5..0a96469fd4 100644
--- a/drivers/mmc/core/sdio.c
+++ b/drivers/mmc/core/sdio.c
@@ -665,6 +665,7 @@ static int mmc_sdio_init_card(struct mmc_host *host, u32 ocr,
 	int retries = 10;
 	u32 rocr = 0;
 	u32 ocr_card = ocr;
+	bool skip_cmd11 = false;
 
 	WARN_ON(!host->claimed);
 
@@ -737,14 +738,23 @@ static int mmc_sdio_init_card(struct mmc_host *host, u32 ocr,
 	 * 1.8v, the card sets S18A to 0 in the R4 response. So it will
 	 * fails to check rocr & R4_18V_PRESENT,  but we still need to
 	 * try to init uhs card. sdio_read_cccr will take over this task
-	 * to make sure which speed mode should work.
+	 * to make sure which speed mode should work. Some cards (RTL8822CS)
+	 * set S18A regardless and then fail CMD11; if that happens at 1.8V,
+	 * retry without it.
 	 */
-	if (rocr & ocr & R4_18V_PRESENT) {
+	if ((rocr & ocr & R4_18V_PRESENT) && !skip_cmd11) {
 		err = mmc_set_uhs_voltage(host, ocr_card);
 		if (err == -EAGAIN) {
 			mmc_sdio_pre_init(host, ocr_card, card);
 			retries--;
 			goto try_again;
+		} else if (err &&
+			   host->ios.signal_voltage == MMC_SIGNAL_VOLTAGE_180) {
+			pr_warn("%s: CMD11 failed at 1.8V, retrying without it\n",
+				mmc_hostname(host));
+			skip_cmd11 = true;
+			mmc_sdio_pre_init(host, ocr_card, card);
+			goto try_again;
 		} else if (err) {
 			ocr &= ~R4_18V_PRESENT;
 		}
-- 
2.53.0