From e45a1bd20fa5b920901879e85cdf5eda21f78d7c Mon Sep 17 00:00:00 2001 From: Philip Langdale Date: Sun, 29 Oct 2006 10:14:19 +0100 Subject: [PATCH] mmc: Add support for mmc v4 wide-bus modes This change adds support for the mmc4 4-bit wide-bus mode. The mmc4 spec defines 8-bit and 4-bit transfer modes. As we do not support any 8-bit hardware, this patch only adds support for the 4-bit mode, but it can easily be built upon when the time comes. The 4-bit mode is electrically compatible with SD's 4-bit mode but the procedure for turning it on is different. This patch implements only the essential parts of the procedure as defined by the spec. Two additional steps are recommended but not compulsory. I am documenting them here so that there's a record. 1) A bus-test mechanism is implemented using dedicated mmc commands which allow for testing the functionality of the data bus at the electrical level. This is pretty paranoid and they way the commands work is not compatible with the mmc subsystem (they don't set valid CRC values). 2) MMC v4 cards can indicate they would like to draw more than the default amount of current in wide-bus modes. We currently will never switch the card into a higher draw mode. Supposedly, allowing the card to draw more current will let it perform better, but the specs seem to indicate that the card will function correctly without the mode change. Empirical testing supports this interpretation. Signed-off-by: Philip Langdale Signed-off-by: Pierre Ossman --- drivers/mmc/mmc.c | 51 ++++++++++++++++++++++++++---------- include/linux/mmc/protocol.h | 5 ++++ 2 files changed, 42 insertions(+), 14 deletions(-) diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c index 2d5b93000dee..1593a6a632cf 100644 --- a/drivers/mmc/mmc.c +++ b/drivers/mmc/mmc.c @@ -397,23 +397,23 @@ static int mmc_select_card(struct mmc_host *host, struct mmc_card *card) return err; /* - * Default bus width is 1 bit. - */ - host->ios.bus_width = MMC_BUS_WIDTH_1; - - /* - * We can only change the bus width of the selected - * card so therefore we have to put the handling + * We can only change the bus width of SD cards when + * they are selected so we have to put the handling * here. + * + * The card is in 1 bit mode by default so + * we only need to change if it supports the + * wider version. */ - if (host->caps & MMC_CAP_4_BIT_DATA) { + if (mmc_card_sd(card) && + (card->scr.bus_widths & SD_SCR_BUS_WIDTH_4)) { + /* - * The card is in 1 bit mode by default so - * we only need to change if it supports the - * wider version. - */ - if (mmc_card_sd(card) && - (card->scr.bus_widths & SD_SCR_BUS_WIDTH_4)) { + * Default bus width is 1 bit. + */ + host->ios.bus_width = MMC_BUS_WIDTH_1; + + if (host->caps & MMC_CAP_4_BIT_DATA) { struct mmc_command cmd; cmd.opcode = SD_APP_SET_BUS_WIDTH; cmd.arg = SD_BUS_WIDTH_4; @@ -1055,6 +1055,29 @@ static void mmc_process_ext_csds(struct mmc_host *host) } mmc_card_set_highspeed(card); + + /* Check for host support for wide-bus modes. */ + if (!(host->caps & MMC_CAP_4_BIT_DATA)) { + continue; + } + + /* Activate 4-bit support. */ + cmd.opcode = MMC_SWITCH; + cmd.arg = (MMC_SWITCH_MODE_WRITE_BYTE << 24) | + (EXT_CSD_BUS_WIDTH << 16) | + (EXT_CSD_BUS_WIDTH_4 << 8) | + EXT_CSD_CMD_SET_NORMAL; + cmd.flags = MMC_RSP_R1B | MMC_CMD_AC; + + err = mmc_wait_for_cmd(host, &cmd, CMD_RETRIES); + if (err != MMC_ERR_NONE) { + printk("%s: failed to switch card to " + "mmc v4 4-bit bus mode.\n", + mmc_hostname(card->host)); + continue; + } + + host->ios.bus_width = MMC_BUS_WIDTH_4; } kfree(ext_csd); diff --git a/include/linux/mmc/protocol.h b/include/linux/mmc/protocol.h index 311b6547f561..45c51fd85786 100644 --- a/include/linux/mmc/protocol.h +++ b/include/linux/mmc/protocol.h @@ -256,6 +256,7 @@ struct _mmc_csd { * EXT_CSD fields */ +#define EXT_CSD_BUS_WIDTH 183 /* R/W */ #define EXT_CSD_HS_TIMING 185 /* R/W */ #define EXT_CSD_CARD_TYPE 196 /* RO */ @@ -270,6 +271,10 @@ struct _mmc_csd { #define EXT_CSD_CARD_TYPE_26 (1<<0) /* Card can run at 26MHz */ #define EXT_CSD_CARD_TYPE_52 (1<<1) /* Card can run at 52MHz */ +#define EXT_CSD_BUS_WIDTH_1 0 /* Card is in 1 bit mode */ +#define EXT_CSD_BUS_WIDTH_4 1 /* Card is in 4 bit mode */ +#define EXT_CSD_BUS_WIDTH_8 2 /* Card is in 8 bit mode */ + /* * MMC_SWITCH access modes */