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mmc: core: Prevent violation of specs while initializing cards

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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>
This commit is contained in:
Ulf Hansson 2013-09-16 11:28:42 +02:00 • committed by Chris Ball
parent 6904115095
commit ce69d37b7d
4 changed files with 13 additions and 37 deletions
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1
drivers/mmc/core/sd.c
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@ -1103,7 +1103,6 @@ static int mmc_sd_resume(struct mmc_host *host)
mmc_claim_host(host);
mmc_power_up(host, host->card->ocr);
mmc_select_voltage(host, host->card->ocr);
err = mmc_sd_init_card(host, host->card->ocr, host->card);
mmc_release_host(host);