Hi Johannes, Johannes Stezenbach wrote: > On Thu, Aug 30, 2012 at 03:08:19PM +0200, Juergen Beisert wrote: > > Johannes Stezenbach wrote: > > > MMC has the following speed modes: > > > > > > - legacy 0-26MHz > > > - high speed SDR 0-52MHz > > > - high speed DDR 0-52MHz > > > - HS200 SDR 0-200MHz > > > > Ahh, here come the curious 26 MHz and 52 MHz into the game. Its related > > to MMC only. > > > > > 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); > > > > As far as I understand the spec, there is a max. speed field in the CSD > > which tells us the regular max. speed of this card. And the fields from > > the CSR can overwrite the CSD settings. So, a card which reports 25 MHz > > in the CSD can still enable 50 MHz (SDR50) in the CSR and the SDHC then > > can use 50 MHz for the clock. But maybe I'm wrong here. > > What I wrote is not even correct ;-/ > > SD has legacy Default Mode and legacy High Speed mode, > and "Ultra High Speed" modes. SDR12, SDR25, SDR50, SDR104 and DDR50 > are all UHS modes. And Default Mode and SDR12 support up to 12.5MB/s, > but the bus clock is up to 25MHz (4 bit parallel). > So the code in mci_startup_sd() is correct as is. Now I found the Abbreviations in the spec: UHS Ultra High Speed SDR12 One of UHS modes with single data rate. Up to 12.5MB/sec at 25MHz SDR25 One of UHS modes with single data rate. Up to 25MB/sec at 50MHz SDR50 One of UHS modes with single data rate. Up to 50MB/sec at 100MHz SDR104 One of UHS modes with single data rate. Up to 104MB/sec at 208MHz So they mean the transfer capacity in "bytes per second" and not the clock speed with their SDR<number>. Thanks for this hint. Reading further discovers: * all these UHS modes are _not_ valid for SDSC type of SD cards (up to 2 GiB capacity) This information should help to get the code right. > Regarding CSD, my understanding is that TRAN_SPEED only > applies to legacy Default Mode. If the card supports HS mode > or UHS modes then it must be able to use 50MHz clock. Ack. Regards, Juergen -- Pengutronix e.K. | Juergen Beisert | Linux Solutions for Science and Industry | http://www.pengutronix.de/ | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
