mmc: core: Prevent violation of specs while initializing cards

According to eMMC/SD/SDIO specs, the VDD (VCC) voltage level must be
maintained during the initialization sequence. If we want/need to tune
the voltage level, a complete power cycle of the card must be executed.

Most host drivers conforms to the specifications by only allowing to
change VDD voltage level at the MMC_POWER_UP state, but some also cares
about MMC_POWER_ON state, which they should'nt. This patch will not
break those drivers, but they could clean up code to better reflect
what is expected from the protocol layer.

A big re-work of the mmc_select_voltage function is done to only change
VDD voltage level if the host supports MMC_CAP2_FULL_PWR_CYCLE.
Otherwise only validation of the host and card ocr mask will be done.

A very nice side-effect of this patch is that we now don't need to
reset the negotiated ocr mask at the mmc_power_off function, since now
it will actually reflect the present voltage level, which safely can be
used at the next power up and re-initialization. Moreover, we then only
need to execute mmc_select_voltage from the attach sequence.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 11 insertions, 20 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 529d2eff6095..63672aba0e98 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1358,21 +1358,20 @@ u32 mmc_select_voltage(struct mmc_host *host, u32 ocr)
         int bit;
 
         ocr &= host->ocr_avail;
+        if (!ocr) {
+                dev_warn(mmc_dev(host), "no support for card's volts\n");
+                return 0;
+        }
 
-        bit = ffs(ocr);
-        if (bit) {
-                bit -= 1;
-
+        if (host->caps2 & MMC_CAP2_FULL_PWR_CYCLE) {
+                bit = ffs(ocr) - 1;
                 ocr &= 3 << bit;
-
-                mmc_host_clk_hold(host);
-                host->ios.vdd = bit;
-                mmc_set_ios(host);
-                mmc_host_clk_release(host);
+                mmc_power_cycle(host, ocr);
         } else {
-                pr_warning("%s: host doesn't support card's voltages\n",
-                                mmc_hostname(host));
-                ocr = 0;
+                bit = fls(ocr) - 1;
+                ocr &= 3 << bit;
+                if (bit != host->ios.vdd)
+                        dev_warn(mmc_dev(host), "exceeding card's volts\n");
         }
 
         return ocr;
@@ -1571,14 +1570,6 @@ void mmc_power_off(struct mmc_host *host)
         host->ios.clock = 0;
         host->ios.vdd = 0;
 
-
-        /*
-         * Reset ocr mask to be the highest possible voltage supported for
-         * this card. This value will be used at next power up.
-         */
-        if (host->card)
-                host->card->ocr = 1 << (fls(host->ocr_avail) - 1);
-
         if (!mmc_host_is_spi(host)) {
                 host->ios.bus_mode = MMC_BUSMODE_OPENDRAIN;
                 host->ios.chip_select = MMC_CS_DONTCARE;