Although the "SD Host Controller Simplified Specification Version 2.00" does not clearly document support for 8-bit bus width, it does show an "Extended Data Transfer Width" field in bit-5 of the Host Control Register. Furthermore, while googling around for more details on this feature, I came across the "MMC: MMC/SD/CE-ATA/SDIO driver for Intel Moorestown platform" [1] which implements 8-bit bus width support but was rejected for other reasons. My experimentation has revealed that setting the "Extended Data Transfer Width" bit in addition to the "Data Transfer Width" bit as done in [1] does in fact enable 8-bit mode. Alas, we need a better method of specifying host capabilities for the myriad SDHCI based devices, e.g. passing host capabilities into sdhci_add_host() via platform data as done for other host drivers. Resolving this host capabilities issue via platform data may also eliminate the need for some of the quirks, e.g. SDHCI_QUIRK_FORCE_1_BIT_DATA would not be necessary if platform data specifies bus_width = 1, etc.,.
Comments and/or feedback greatly appreciated. [1] http://patchwork.kernel.org/patch/20993/ Signed-off-by: George G. Davis <[email protected]> Cc: JiebingLi <[email protected]> Cc: FengTang <[email protected]> Cc: GermanMonroy <[email protected]> --- drivers/mmc/host/sdhci.c | 17 ++++++++++++++--- drivers/mmc/host/sdhci.h | 1 + 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c index 6c2978c..6c05d80 100644 --- a/drivers/mmc/host/sdhci.c +++ b/drivers/mmc/host/sdhci.c @@ -1147,10 +1147,19 @@ static void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios) ctrl = sdhci_readb(host, SDHCI_HOST_CONTROL); - if (ios->bus_width == MMC_BUS_WIDTH_4) + switch (ios->bus_width) { + case MMC_BUS_WIDTH_8: ctrl |= SDHCI_CTRL_4BITBUS; - else + ctrl |= SDHCI_CTRL_8BITBUS; + break; + case MMC_BUS_WIDTH_4: + ctrl |= SDHCI_CTRL_4BITBUS; + ctrl &= ~SDHCI_CTRL_8BITBUS; + break; + default: ctrl &= ~SDHCI_CTRL_4BITBUS; + ctrl &= ~SDHCI_CTRL_8BITBUS; + } if (ios->timing == MMC_TIMING_SD_HS) ctrl |= SDHCI_CTRL_HISPD; @@ -1783,8 +1792,10 @@ int sdhci_add_host(struct sdhci_host *host) mmc->f_max = host->max_clk; mmc->caps = MMC_CAP_SDIO_IRQ; - if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA)) + if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA)) { mmc->caps |= MMC_CAP_4_BIT_DATA; + mmc->caps |= MMC_CAP_8_BIT_DATA; + } if (caps & SDHCI_CAN_DO_HISPD) mmc->caps |= MMC_CAP_SD_HIGHSPEED; diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h index 9ba4268..6bd46e5 100644 --- a/drivers/mmc/host/sdhci.h +++ b/drivers/mmc/host/sdhci.h @@ -72,6 +72,7 @@ #define SDHCI_CTRL_ADMA1 0x08 #define SDHCI_CTRL_ADMA32 0x10 #define SDHCI_CTRL_ADMA64 0x18 +#define SDHCI_CTRL_8BITBUS 0x20 #define SDHCI_POWER_CONTROL 0x29 #define SDHCI_POWER_ON 0x01 -- 1.6.3.3.311.g43dd -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
