Hi, 2014-11-21 1:51 GMT+01:00 Vincent Yang <vincent.yang.fujitsu@xxxxxxxxx>: > Voltage Switch Procedure > > 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> Reviewed-by: Johan Rudholm <jrudholm@xxxxxxxxx> BR, Johan -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
