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authorPhilip Langdale <philipl@overt.org>2006-10-29 10:14:19 +0100
committerPierre Ossman <drzeus@drzeus.cx>2006-12-01 18:22:44 +0100
commite45a1bd20fa5b920901879e85cdf5eda21f78d7c (patch)
treed767af9df9ae4b39e9bd3675b1644fa5eaccd325 /drivers/mmc
parentbce40a36de574376f41f1ff3c4d212a7da2a3c90 (diff)
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 <philipl@overt.org> Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Diffstat (limited to 'drivers/mmc')
-rw-r--r--drivers/mmc/mmc.c51
1 files changed, 37 insertions, 14 deletions
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 2d5b93000de..1593a6a632c 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);