[PATCH 05/10] mci: add HS400 Enhanced Strobe (HS400ES) selection
Sascha Hauer
s.hauer at pengutronix.de
Mon May 11 05:08:00 PDT 2026
HS400ES bypasses HS200 tuning entirely: the eMMC drives a data strobe
line which the controller samples on, so the read path doesn't need
software-tuned phase. It still ends up in MMC_TIMING_MMC_HS400.
Detection: a card advertises HS400ES via EXT_CSD_STROBE_SUPPORT[184],
which sits outside DEVICE_TYPE; record it as a synthetic
EXT_CSD_CARD_TYPE_HS400ES bit in mmc_avail_type when the host
declares MMC_CAP2_HS400_ES (mmc-hs400-enhanced-strobe in DT) and the
card has both STROBE_SUPPORT set and one of the HS400 voltage variants.
Transition (mmc_select_hs400es):
1. Negotiate 8-bit bus in HS mode (HS400 needs 8-bit).
2. CMD6 EXT_CSD_HS_TIMING = HS, host to HS rate.
3. CMD6 EXT_CSD_BUS_WIDTH = 8-bit DDR | STROBE bit, so the card
starts driving the strobe line.
4. CMD6 EXT_CSD_HS_TIMING = HS400, host to HS400 timing at
hs200_max_dtr (200 MHz, DDR-sampled => 400 MT/s).
5. Call host->ops.hs400_enhanced_strobe so the controller enables
enhanced strobe sampling.
mmc_select_timing prefers HS400ES over HS200 + HS400; on any failure
it clears the flag and falls back to HS200. mci_startup_mmc returns
early when mmc_select_timing already landed us in HS400 (HS400ES has
no follow-up tuning step).
mci_ops gains an optional hs400_enhanced_strobe hook for the
controller's enhanced-strobe enable.
Assisted-by: Claude Opus 4.7 <noreply at anthropic.com>
Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
drivers/mci/mci-core.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++-
include/mci.h | 4 ++
2 files changed, 111 insertions(+), 1 deletion(-)
diff --git a/drivers/mci/mci-core.c b/drivers/mci/mci-core.c
index 58b28ec653..0cfddb8d43 100644
--- a/drivers/mci/mci-core.c
+++ b/drivers/mci/mci-core.c
@@ -1798,6 +1798,16 @@ static void mmc_select_max_dtr(struct mci *mci)
avail_type |= EXT_CSD_CARD_TYPE_HS400_1_2V;
}
+ /*
+ * HS400ES capability is reported in EXT_CSD_STROBE_SUPPORT (byte 184),
+ * not in DEVICE_TYPE. Combine with one of the HS400 voltage variants;
+ * which voltage is used follows the same negotiation as HS400.
+ */
+ if ((caps2 & MMC_CAP2_HS400_ES) &&
+ mci->ext_csd[EXT_CSD_STROBE_SUPPORT] &&
+ (avail_type & EXT_CSD_CARD_TYPE_HS400))
+ avail_type |= EXT_CSD_CARD_TYPE_HS400ES;
+
mci->host->hs200_max_dtr = hs200_max_dtr;
mci->host->hs_max_dtr = hs_max_dtr;
mci->host->mmc_avail_type = avail_type;
@@ -1901,6 +1911,83 @@ static void mmc_set_bus_speed(struct mci *mci)
mci_set_clock(mci, max_dtr);
}
+/*
+ * Switch directly to HS400 with Enhanced Strobe per JEDEC. Unlike plain
+ * HS400 this does not require HS200 tuning first - the controller samples
+ * data using the eMMC-driven strobe line. The transition is:
+ *
+ * 1. Negotiate 8-bit bus width in HS mode.
+ * 2. Switch the card to HS timing.
+ * 3. Set host to MMC_TIMING_MMC_HS at hs_max_dtr.
+ * 4. Switch card BUS_WIDTH to 8-bit DDR with the STROBE bit set, so
+ * the card drives the strobe line.
+ * 5. Switch the card to HS400 timing.
+ * 6. Switch the host to MMC_TIMING_MMC_HS400 and ramp the clock to
+ * hs200_max_dtr (200 MHz, DDR-sampled => 400 MT/s).
+ * 7. Tell the controller to enable enhanced strobe sampling.
+ */
+static int mmc_select_hs400es(struct mci *mci)
+{
+ struct mci_host *host = mci->host;
+ int err;
+ u8 val;
+
+ /* Step 1: 8-bit bus is mandatory for HS400ES */
+ err = mci_mmc_try_bus_width(mci, MMC_BUS_WIDTH_8, MMC_TIMING_MMC_HS);
+ if (err < 0) {
+ dev_err(&mci->dev, "HS400ES requires 8-bit bus width\n");
+ return err;
+ }
+
+ /* Step 2: switch card to HS timing */
+ err = mci_switch(mci, EXT_CSD_HS_TIMING, EXT_CSD_TIMING_HS);
+ if (err) {
+ dev_err(&mci->dev, "switch to HS for HS400ES failed: %d\n", err);
+ return err;
+ }
+
+ /* Step 3: host follows to HS rate */
+ mci_set_timing(mci, MMC_TIMING_MMC_HS);
+ mci_set_clock(mci, host->hs_max_dtr);
+
+ err = mci_switch_status(mci, true);
+ if (err)
+ return err;
+
+ /* Step 4: 8-bit DDR with strobe enabled */
+ val = EXT_CSD_DDR_BUS_WIDTH_8 | EXT_CSD_BUS_WIDTH_STROBE;
+ err = mci_switch(mci, EXT_CSD_BUS_WIDTH, val);
+ if (err) {
+ dev_err(&mci->dev, "switch to DDR8 with strobe failed: %d\n", err);
+ return err;
+ }
+
+ /* Step 5: switch card to HS400 */
+ val = EXT_CSD_TIMING_HS400 | (host->drive_strength << EXT_CSD_DRV_STR_SHIFT);
+ err = mci_switch(mci, EXT_CSD_HS_TIMING, val);
+ if (err) {
+ dev_err(&mci->dev, "switch to HS400 for HS400ES failed: %d\n", err);
+ return err;
+ }
+
+ /* Step 6: host to HS400 timing and final clock */
+ mci_set_timing(mci, MMC_TIMING_MMC_HS400);
+ mmc_set_bus_speed(mci);
+
+ err = mci_switch_status(mci, true);
+ if (err)
+ return err;
+
+ /* Step 7: enable enhanced strobe in the controller */
+ host->ios.enhanced_strobe = true;
+ if (host->ops.hs400_enhanced_strobe)
+ host->ops.hs400_enhanced_strobe(host, &host->ios);
+
+ dev_dbg(&mci->dev, "HS400ES selected\n");
+
+ return 0;
+}
+
/*
* Activate HS200 or HS400ES mode if supported.
*/
@@ -1910,6 +1997,20 @@ int mmc_select_timing(struct mci *mci)
mmc_select_max_dtr(mci);
+ /*
+ * HS400ES is the preferred path when both card and host support it:
+ * it ends up in HS400 without needing HS200 tuning. If the transition
+ * fails for any reason, drop the flag and fall through to HS200/HS400.
+ */
+ if (mci->host->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
+ err = mmc_select_hs400es(mci);
+ if (!err)
+ goto out;
+ dev_dbg(&mci->dev, "HS400ES failed (%d), trying HS200\n", err);
+ mci->host->mmc_avail_type &= ~EXT_CSD_CARD_TYPE_HS400ES;
+ err = 0;
+ }
+
if (mci->host->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200) {
err = mmc_select_hs200(mci);
if (err == -EBADMSG)
@@ -2014,6 +2115,10 @@ static int mci_startup_mmc(struct mci *mci)
if (ret)
return ret;
+ /* HS400ES took us straight to HS400 without tuning. Done. */
+ if (mmc_card_hs400(mci))
+ return 0;
+
if (mmc_card_hs200(mci)) {
ret = mmc_hs200_tuning(mci);
if (!ret) {
@@ -2698,7 +2803,8 @@ static void mci_info(struct device *dev)
bw = 1;
printf(" current buswidth: %d\n", bw);
- printf(" current timing: %s\n", mci_timing_tostr(host->ios.timing));
+ printf(" current timing: %s%s\n", mci_timing_tostr(host->ios.timing),
+ host->ios.enhanced_strobe ? " (Enhanced Strobe)" : "");
mci_print_caps(host->host_caps, host->caps2);
printf("Card information:\n");
diff --git a/include/mci.h b/include/mci.h
index a7cd0c5ae2..7a86a80b03 100644
--- a/include/mci.h
+++ b/include/mci.h
@@ -406,6 +406,7 @@
#define EXT_CSD_DDR_BUS_WIDTH_4 5 /* Card is in 4 bit DDR mode */
#define EXT_CSD_DDR_BUS_WIDTH_8 6 /* Card is in 8 bit DDR mode */
#define EXT_CSD_DDR_FLAG BIT(2) /* Flag for DDR mode */
+#define EXT_CSD_BUS_WIDTH_STROBE BIT(7) /* Enhanced strobe mode (HS400ES) */
#define EXT_CSD_TIMING_BC 0 /* Backwards compatility */
#define EXT_CSD_TIMING_HS 1 /* High speed */
@@ -567,6 +568,7 @@ struct mci_ios {
enum mci_bus_width bus_width; /* data bus width */
enum mci_timing timing; /* timing specification used */
unsigned char drv_type; /* driver type (A, B, C, D) */
+ bool enhanced_strobe; /* HS400ES selected */
};
struct mci;
@@ -586,6 +588,8 @@ struct mci_ops {
/* The tuning command opcode value is different for SD and eMMC cards */
int (*execute_tuning)(struct mci_host *, u32);
void (*set_uhs_signaling)(struct mci_host *host, unsigned int timing);
+ /* Enable enhanced strobe in the controller (HS400ES) */
+ void (*hs400_enhanced_strobe)(struct mci_host *, struct mci_ios *);
};
/** host information */
--
2.47.3
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