Hi Krunal,
sorry for delay.
On 04/25/2014 06:19 PM, Krunal Desai wrote:
Hi all -
I noticed that in zynq_sdhci.c, responsible for initializing PS SD controller(s), host controller max clock frequency is always set to 52MHz (http://git.denx.de/?p=u-boot.git;a=blob;f=drivers/mmc/zynq_sdhci.c;h=fdce2c2...). In cases where user is using EMIO connectivity, max clock speed is limited to 25MHz. This results in out-of-spec operation as the divider calculation logic trusts the input to add_sdhci() and does not check the SLCR itself to confirm what the IO clock to SD controller actually is.
I think I saw OF/device-tree support patched in recently (I am on the 2013.4 tag); I think the "right" way to solve this is add capability in zynq_sdhci_init to read device-tree for 'clock-frequency' property, and use that to populate the arguments to add_sdhci() with that information, defaulting to a safe minimum (25MHz?) if no entry is found. Otherwise, I suppose a config could be added akin to 'ZYNQ_SD0_MIO'/'ZYNQ_SD1_MIO' to populate the correct minimum value.
Does this sound sane? I am thinking of implementing that as a patch for ourselves internally, but I think it will be of value to the greater community as well.
we didn't test this configuration that's why 52MHz is there as default case. I think that should be easily possible to detect MIO setting as we are doing for qspi/nand/usb.
We have this code in our xilinx repository and I have sent patches for mainline review 2 weeks ago or something like that. I haven't got any NACK and I am going to send pull request to ARM custodian when I fix fpga patches.
It means detection via MIO setting is reasonable way how to do it. When you know that this go through EMIO 25MHz should be used.
Thanks, Michal