This patch is to fix an issue found on mb86s7x platforms. [symptom] There are some UHS-1 SD memory cards sometimes cannot be detected correctly, e.g., Transcend 600x SDXC 64GB UHS-1 memory card. During Signal Voltage Switch Procedure, failure to switch is indicated by the card holding DAT[3:0] low. [analysis] According to SD Host Controller Simplified Specification Version 3.00 chapter 3.6.1, the Signal Voltage Switch Procedure should be: (1) Check S18A; (2) Issue CMD11; (3) Check CMD 11 response; (4) Stop providing SD clock; (5) Check DAT[3:0] should be 0000b; (6) Set 1.8V Signal Enable; (7) Wait 5ms; (8) Check 1.8V Signal Enable; (9) Provide SD Clock; (10) Wait 1ms; (11) Check DAT[3:0] should be 1111b; (12) error handling With CONFIG_MMC_CLKGATE=y, sometimes there is one more gating/un-gating SD clock between (2) and (3). In this case, some UHS-1 SD cards will hold DAT[3:0] 0000b at (11) and thus fails Signal Voltage Switch Procedure. [solution] By mmc_host_clk_hold() before CMD11, the additional gating/un-gating SD clock between (2) and (3) can be prevented and thus no failure at (11). It has been verified with many UHS-1 SD cards on mb86s7x platforms and works correctly. Signed-off-by: Vincent Yang <Vincent.Yang@xxxxxxxxxxxxxx> --- drivers/mmc/core/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c index 7dc0c85..764af63 100644 --- a/drivers/mmc/core/core.c +++ b/drivers/mmc/core/core.c @@ -1428,6 +1428,8 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage, u32 ocr) pr_warning("%s: cannot verify signal voltage switch\n", mmc_hostname(host)); + mmc_host_clk_hold(host); + cmd.opcode = SD_SWITCH_VOLTAGE; cmd.arg = 0; cmd.flags = MMC_RSP_R1 | MMC_CMD_AC; @@ -1438,8 +1440,6 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage, u32 ocr) if (!mmc_host_is_spi(host) && (cmd.resp[0] & R1_ERROR)) return -EIO; - - mmc_host_clk_hold(host); /* * The card should drive cmd and dat[0:3] low immediately * after the response of cmd11, but wait 1 ms to be sure -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html