mmc: sd: Handle UHS-I voltage signaling without power cycle

Some boards have SD card connectors where the power rail cannot be switched
off by the driver. However there are various circumstances when a card
might be re-initialized, such as after system resume, warm re-boot, or
error handling. However, a UHS card will continue to use 1.8V signaling
unless it is power cycled.

If the card has not been power cycled, it may still be using 1.8V
signaling. According to the SD spec., the Bus Speed Mode (function group 1)
bits 2 to 4 are zero if the card is initialized at 3.3V signal level. Thus
they can be used to determine if the card has already switched to 1.8V
signaling. Detect that situation and try to initialize a UHS-I (1.8V)
transfer mode.

Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 0f07955a32e8bdaa5ed8458f9c94b84f986f1575..bf82c5156003acd0e817aafbbd79b869a4f934af 100644 (file)
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -643,6 +643,19 @@ static int mmc_switch_voltage(struct mmc *mmc, int signal_voltage)
 
        return 0;
 }
+
+static bool mmc_sd_card_using_v18(struct mmc *mmc)
+{
+       /*
+        * According to the SD spec., the Bus Speed Mode (function group 1) bits
+        * 2 to 4 are zero if the card is initialized at 3.3V signal level. Thus
+        * they can be used to determine if the card has already switched to
+        * 1.8V signaling.
+        */
+       bool volt = mmc->sd3_bus_mode &
+              (SD_MODE_UHS_SDR50 | SD_MODE_UHS_SDR104 | SD_MODE_UHS_DDR50);
+       return volt;
+}
 #endif
 
 static int sd_send_op_cond(struct mmc *mmc, bool uhs_en)
@@ -1369,9 +1382,6 @@ static int sd_get_capabilities(struct mmc *mmc)
        ALLOC_CACHE_ALIGN_BUFFER(__be32, switch_status, 16);
        struct mmc_data data;
        int timeout;
-#if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
-       u32 sd3_bus_mode;
-#endif
 
        mmc->card_caps = MMC_MODE_1BIT | MMC_CAP(MMC_LEGACY);
 
@@ -1451,16 +1461,16 @@ static int sd_get_capabilities(struct mmc *mmc)
        if (mmc->version < SD_VERSION_3)
                return 0;
 
-       sd3_bus_mode = __be32_to_cpu(switch_status[3]) >> 16 & 0x1f;
-       if (sd3_bus_mode & SD_MODE_UHS_SDR104)
+       mmc->sd3_bus_mode = __be32_to_cpu(switch_status[3]) >> 16 & 0x1f;
+       if (mmc->sd3_bus_mode & SD_MODE_UHS_SDR104)
                mmc->card_caps |= MMC_CAP(UHS_SDR104);
-       if (sd3_bus_mode & SD_MODE_UHS_SDR50)
+       if (mmc->sd3_bus_mode & SD_MODE_UHS_SDR50)
                mmc->card_caps |= MMC_CAP(UHS_SDR50);
-       if (sd3_bus_mode & SD_MODE_UHS_SDR25)
+       if (mmc->sd3_bus_mode & SD_MODE_UHS_SDR25)
                mmc->card_caps |= MMC_CAP(UHS_SDR25);
-       if (sd3_bus_mode & SD_MODE_UHS_SDR12)
+       if (mmc->sd3_bus_mode & SD_MODE_UHS_SDR12)
                mmc->card_caps |= MMC_CAP(UHS_SDR12);
-       if (sd3_bus_mode & SD_MODE_UHS_DDR50)
+       if (mmc->sd3_bus_mode & SD_MODE_UHS_DDR50)
                mmc->card_caps |= MMC_CAP(UHS_DDR50);
 #endif
 
@@ -1830,7 +1840,11 @@ static int sd_select_mode_and_width(struct mmc *mmc, uint card_caps)
        uint widths[] = {MMC_MODE_4BIT, MMC_MODE_1BIT};
        const struct mode_width_tuning *mwt;
 #if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
-       bool uhs_en = (mmc->ocr & OCR_S18R) ? true : false;
+       /*
+        * Enable UHS mode if the card advertises 1.8V support (S18R in OCR)
+        * or is already operating at 1.8V signaling.
+        */
+       bool uhs_en = (mmc->ocr & OCR_S18R) || mmc_sd_card_using_v18(mmc);
 #else
        bool uhs_en = false;
 #endif
@@ -2701,6 +2715,27 @@ static int mmc_startup(struct mmc *mmc)
                err = sd_get_capabilities(mmc);
                if (err)
                        return err;
+
+#if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
+               /*
+                * If the card has already switched to 1.8V signaling, then
+                * set the signal voltage to 1.8V.
+                */
+               if (mmc_sd_card_using_v18(mmc)) {
+                       /*
+                        * During a signal voltage level switch, the clock must be gated
+                        * for 5 ms according to the SD spec.
+                        */
+                       mmc_set_clock(mmc, mmc->clock, MMC_CLK_DISABLE);
+                       err = mmc_set_signal_voltage(mmc, MMC_SIGNAL_VOLTAGE_180);
+                       if (err)
+                               return err;
+                       /* Keep clock gated for at least 10 ms, though spec only says 5 ms */
+                       mdelay(10);
+                       mmc_set_clock(mmc, mmc->clock, MMC_CLK_ENABLE);
+               }
+#endif
+
                err = sd_select_mode_and_width(mmc, mmc->card_caps);
        } else {
                err = mmc_get_capabilities(mmc);

diff --git a/include/mmc.h b/include/mmc.h
index c6b2ab4a29fb9accedaa2a5cbb8ee36d90423eee..51d3f2f8dd599d82ef4e2c33068479cce8f23f8f 100644 (file)
--- a/include/mmc.h
+++ b/include/mmc.h
@@ -759,6 +759,9 @@ struct mmc {
 #endif
        u8 *ext_csd;
        u32 cardtype;           /* cardtype read from the MMC */
+#if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
+       u32 sd3_bus_mode;       /* Supported UHS-I bus speed modes */
+#endif
        enum mmc_voltage current_voltage;
        enum bus_mode selected_mode; /* mode currently used */
        enum bus_mode best_mode; /* best mode is the supported mode with the