Hi, On Wed, Aug 29, 2012 at 11:17:03PM +0200, Juergen Beisert wrote: > any SD/MMC card experts here? I have trouble with the current SD/MMC > detection > code in Barebox. > The function sd_change_freq() in the file 'drivers/mci/mci-core.c' tries to > detect the max. transfer frequency the attached card can handle. Nothing > special here, but the following line in this routine fails on my system: > > if ((__be32_to_cpu(switch_status[4]) & 0x0f000000) == 0x01000000) > > It checks the clock speed capabilities returned from the card. As far as I > understand the "simplified SD card spec" the "0x01000000" means SDR25 speed,
I think your analysis is correct. > which means still "single transfer per clock at 25 MHz clock rate". But the > sd_change_freq() routine sets the MMC_MODE_HS bit for this case in the card's > capabilities variable. The remaining routines in 'drivers/mci/mci-core.c' > then use 50 MHz for the transfer speed. IMHO mci_startup_sd() is buggy. > This behaviour became an issue here, as my SDHC supports 50 MHz, but the > attached card only up to 25 MHz. After switching to 50 MHz, the card wasn't > able to respond anymore. > For SDHCs which supports only up to 25 MHz this misinterpretation is no > issue, > as the routines still use the 25 MHz, and the SD card can still respond. > > "simplified SD card spec" talks about the bit's meaning: seems the regular > speed was SDR12 which means 12.5 MHz. Then SDR25 cards appear, which are also > called "high speed card". Could the MMC_MODE_HS just mean this "high speed" > and using it at 50 MHz is just some kind of typo? Or do MMCs act differently > and the code mixes SD and MMC features? > > Any pointers would help. MMC has the following speed modes: - legacy 0-26MHz - high speed SDR 0-52MHz - high speed DDR 0-52MHz - HS200 SDR 0-200MHz while SD has: - SDR12 - SDR25 - SDR50 - SDR104 - DDR50 So my guess is that MMC_MODE_HS maps to SDR25 for SD-only, and MMC_MODE_HS_52MHz maps to SDR50 for SD and MMC. (Apparently mmc_change_freq always sets MMC_MODE_HS, it is meaningless for MMC.) Thus, mci_startup_sd() should do: if (mci->card_caps & MMC_MODE_HS) mci_set_clock(mci, 25000000); else mci_set_clock(mci, 12500000); Johannes _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox