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SubjectRe: A MMC card transfer issue
From
2010/11/9 Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>:
> I am facing the issue about some MMC cards on Intel EG20T PCH (Platform Controller Hub).
> The linux version is 2.6.36.
> I can not transfer data the MMC cards (e.g. Transcned MMC card).
> The card is 1 bit bus width. And the card is according to MMC specification V3.x.
> And the EG20T has a 4 bit bus width capability
> Linux MMC standard driver decides the card bus width as 4 bit,
> if the MMC specification version is larger than or equal to V4.0 like below.
>
> linux/drivers/mmc/core/mmc.c
>
>  505        /*
>  506         * Activate wide bus (if supported).
>  507         */
>  508        if ((card->csd.mmca_vsn >= CSD_SPEC_VER_4) &&
>  509            (host->caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA))) {
>  510                unsigned ext_csd_bit, bus_width;
>  511
>  512                if (host->caps & MMC_CAP_8_BIT_DATA) {
>  513                        ext_csd_bit = EXT_CSD_BUS_WIDTH_8;
>  514                        bus_width = MMC_BUS_WIDTH_8;
>  515                } else {
>  516                        ext_csd_bit = EXT_CSD_BUS_WIDTH_4;
>  517                        bus_width = MMC_BUS_WIDTH_4;
>  518                }
>  519
>  520                err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>  521                                 EXT_CSD_BUS_WIDTH, ext_csd_bit);
>  522
>  523                if (err && err != -EBADMSG)
>  524                        goto free_card;
>  525
>  526                if (err) {
>  527                        printk(KERN_WARNING "%s: switch to bus width %d "
>  528                               "failed\n", mmc_hostname(card->host),
>  529                               1 << bus_width);
>  530                        err = 0;
>  531                } else {
>  532                        mmc_set_bus_width(card->host, bus_width);
>  533                }
>  534        }
>  535
>
> However the MMC specification version id is the same as V3.x and V4.0.
> Therefore the driver uses the 4 bit bus width for the MMC card
> even if the card has only 1 bit bus width.
> I modified the driver to use 1 bit bus width only tentatively and confirmed that
> we can mount the card and R/W correctly.
>
> I think we can not support MMC_CAP_4_BIT_DATA or MMC_CAP_8_BIT_DATA in MMC V4.0.
>
> How do you think ?

You can find a patch for 4-bit support. the problem is there's some
bug related so it set the 4 & 8 bit support both.
So line 512 is always true. you can just remove the one line like this.

It's quirk-and-dirty patch. now we try to find a generic solution to
solve this issue.
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1849,7 +1849,7 @@ int sdhci_add_host(struct sdhci_host *host)
mmc->caps |= MMC_CAP_SDIO_IRQ;

if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA))
- mmc->caps |= MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA;
+ mmc->caps |= MMC_CAP_4_BIT_DATA;

if (caps & SDHCI_CAN_DO_HISPD)
mmc->caps |= MMC_CAP_SD_HIGHSPEED | MMC_CAP_MMC_HIGHSPEED;
Thank you,
Kyungmin Park
>
> --
> Thanks,
> Tomoya MORINAGA(OKI SEMICONDUCTOR CO., LTD.)
> --
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