On 23:17 Wed 29 Aug , Juergen Beisert wrote: > Hi there, > > 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, > 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. > > 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? I saw it too this isssue the mmc and sd feature are different with different spec so we need different code to interpret it see in the kernel Best Regards, J. _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
