[PATCH] Fix broken bus voltage setting in sdhc

[Ben Pye]

I have been attempting to run OpenBSD on my HP Chromebook 13, it's a
Skylake device with eMMC storage. Previously sdhc attempted to set the
same bus voltage multiple times, and after the first, successful,
attempt it would break resulting in all later commands timing out. This
patch changes sdhc such that it only sets the voltage if the request is
for a different level, this is the behaviour FreeBSD has.

Ben.

Index: sys/dev/sdmmc/sdhc.c
===================================================================
RCS file: /cvs/src/sys/dev/sdmmc/sdhc.c,v
retrieving revision 1.61
diff -u -p -u -p -r1.61 sdhc.c
--- sys/dev/sdmmc/sdhc.c        6 Sep 2018 10:15:17 -0000       1.61
+++ sys/dev/sdmmc/sdhc.c        7 Nov 2018 15:36:10 -0000
@@ -53,6 +53,7 @@ struct sdhc_host {
        u_int8_t regs[14];              /* host controller state */
        u_int16_t intr_status;          /* soft interrupt status */
        u_int16_t intr_error_status;    /* soft error status */
+       u_int8_t vdd;                   /* current vdd */
 
        bus_dmamap_t adma_map;
        bus_dma_segment_t adma_segs[1];
@@ -420,6 +421,8 @@ sdhc_host_reset(sdmmc_chipset_handle_t s
 
        s = splsdmmc();
 
+       hp->vdd = 0;
+
        /* Disable all interrupts. */
        HWRITE2(hp, SDHC_NINTR_SIGNAL_EN, 0);
 
@@ -491,6 +494,16 @@ sdhc_bus_power(sdmmc_chipset_handle_t sc
        int s;
 
        s = splsdmmc();
+
+       /* 
+        * If the requested vdd is the same as current vdd return.
+        */
+       if (hp->vdd == ocr) {
+               splx(s);
+               return 0;
+       }
+
+       hp->vdd = ocr;
 
        /*
         * Disable bus power before voltage change.