mmc: core: properly select voltage range without power cycle

In mmc_select_voltage(), if there is no full power cycle, the voltage
range selected at the end of the function will be on a single range
(e.g. 3.3V/3.4V). To keep a range around the selected voltage (3.2V/3.4V),
the mask shift should be reduced by 1.

This issue was triggered by using a specific SD-card (Verbatim Premium
16GB UHS-1) on an STM32MP157C-DK2 board. This board cannot do UHS modes
and there is no power cycle. And the card was failing to switch to
high-speed mode. When adding the range 3.2V/3.3V for this card with the
proposed shift change, the card can switch to high-speed mode.

Fixes: ce69d37b7d8f ("mmc: core: Prevent violation of specs while initializing cards")
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20221028073740.7259-1-yann.gautier@foss.st.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 95fa8fb1d45f2b5475805147b0bcf40b601abbfd..c5de202f530ae8cb9fb2e6e9acfe1eb2ec8ffd5f 100644 (file)
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -1134,7 +1134,13 @@ u32 mmc_select_voltage(struct mmc_host *host, u32 ocr)
                mmc_power_cycle(host, ocr);
        } else {
                bit = fls(ocr) - 1;
-               ocr &= 3 << bit;
+               /*
+                * The bit variable represents the highest voltage bit set in
+                * the OCR register.
+                * To keep a range of 2 values (e.g. 3.2V/3.3V and 3.3V/3.4V),
+                * we must shift the mask '3' with (bit - 1).
+                */
+               ocr &= 3 << (bit - 1);
                if (bit != host->ios.vdd)
                        dev_warn(mmc_dev(host), "exceeding card's volts\n");
        }