mmc: core: Prepare to support SD UHS-II cards

The SD UHS-II interface was introduced to the SD spec v4.00 several years
ago. The interface is fundamentally different from an electrical and a
protocol point of view, comparing to the legacy SD interface.

However, the legacy SD protocol is supported through a specific transport
layer (SD-TRAN) defined in the UHS-II addendum of the spec. This allows the
SD card to be managed in a very similar way as a legacy SD card, hence a
lot of code can be re-used to support these new types of cards through the
mmc subsystem.

Moreover, an SD card that supports the UHS-II interface shall also be
backwards compatible with the legacy SD interface, which allows a UHS-II
card to be inserted into a legacy slot. As a matter of fact, this is
already supported by mmc subsystem as of today.

To prepare to add support for UHS-II, this change puts the basic foundation
in the mmc core in place, allowing it to be more easily reviewed before
subsequent changes implements the actual support.

Basically, the approach here adds a new UHS-II bus_ops type and adds a
separate initialization path for the UHS-II card. The intent is to avoid us
from sprinkling the legacy initialization path, but also to simplify
implementation of the UHS-II specific bits.

At this point, there is only one new host ops added to manage the various
ios settings needed for UHS-II. Additional host ops that are needed, are
being added from subsequent changes.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20240913102836.6144-3-victorshihgli@gmail.com

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 01a7142eada3..54ca9dc2114c 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2267,6 +2267,18 @@ void mmc_rescan(struct work_struct *work)
 		goto out;
 	}
 
+	/*
+	 * Ideally we should favor initialization of legacy SD cards and defer
+	 * UHS-II enumeration. However, it seems like cards doesn't reliably
+	 * announce their support for UHS-II in the response to the ACMD41,
+	 * while initializing the legacy SD interface. Therefore, let's start
+	 * with UHS-II for now.
+	 */
+	if (!mmc_attach_sd_uhs2(host)) {
+		mmc_release_host(host);
+		goto out;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(freqs); i++) {
 		unsigned int freq = freqs[i];
 		if (freq > host->f_max) {
@@ -2299,10 +2311,13 @@ void mmc_rescan(struct work_struct *work)
 
 void mmc_start_host(struct mmc_host *host)
 {
+	bool power_up = !(host->caps2 &
+			 (MMC_CAP2_NO_PRESCAN_POWERUP | MMC_CAP2_SD_UHS2));
+
 	host->f_init = max(min(freqs[0], host->f_max), host->f_min);
 	host->rescan_disable = 0;
 
-	if (!(host->caps2 & MMC_CAP2_NO_PRESCAN_POWERUP)) {
+	if (power_up) {
 		mmc_claim_host(host);
 		mmc_power_up(host, host->ocr_avail);
 		mmc_release_host(host);