Revisit this patch, since it break one board [1]. [1] https://lore.kernel.org/all/[email protected]/
On Tue, Oct 21, 2025 at 01:45:26PM -0700, Tanmay Kathpalia wrote: >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 <[email protected]> >--- > drivers/mmc/mmc.c | 55 ++++++++++++++++++++++++++++++++++++++--------- > include/mmc.h | 3 +++ > 2 files changed, 48 insertions(+), 10 deletions(-) > >diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c >index ec61ed92e86..e1f62a5d0ad 100644 >--- 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); This is wrong. sd3_bus_mode is sd supported bits, not the current running bits. To detect the sd card running bits, need to use: (__be32_to_cpu(switch_status[4]) >> 24) & 0xF >+ 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); In theory, bool uhs_en = (mmc->ocr & OCR_S18R) ? true : false; is correct. OCR (including S18R/S18A) only reflects voltage switch negotiation capability and intent, not the current signaling voltage. So your sd card should have OCR_S18R returned per my understanding. > #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)) { To switch voltage, ACMD41 is required, see mmc_switch_voltage. Forcing switch to 1.8 here has some risk. >+ /* >+ * 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 A proper redesign is required. So I am going to revert this patch. Thanks Peng
