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 ?
--
Thanks,
Tomoya MORINAGA(OKI SEMICONDUCTOR CO., LTD.)
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