From 6c52ba77797c2ac62dcdb74e1bdd898003b9bc3b Mon Sep 17 00:00:00 2001 From: Aaron Durbin Date: Wed, 16 Oct 2013 09:21:55 -0700 Subject: rambi: disable internal pullups on ram_id[2:0] The ram_id[2:0] signals have stuffing options for pull up/down with values of 10K. However, the default pulldown values for these pads are 20K. Therefore, one can't read a high value because of the high voltage threshold is 0.65 * Vref. Therefore the high signals are marginal at best. Fix this issue by disabling the internal pull for the pads connected to ram_id[2:0]. BUG=chrome-os-partner:23350 BRANCH=None TEST=Built and checked that ram_id[2:0] is properly read now. Change-Id: Ib414d5798b472574337d1b71b87a4cf92f40c762 Signed-off-by: Aaron Durbin Reviewed-on: https://chromium-review.googlesource.com/173211 Reviewed-by: Shawn Nematbakhsh Reviewed-by: Bernie Thompson Reviewed-on: http://review.coreboot.org/4885 Tested-by: build bot (Jenkins) Reviewed-by: Patrick Georgi --- src/mainboard/google/rambi/romstage.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/src/mainboard/google/rambi/romstage.c b/src/mainboard/google/rambi/romstage.c index d15a21dc2d..369ebad445 100644 --- a/src/mainboard/google/rambi/romstage.c +++ b/src/mainboard/google/rambi/romstage.c @@ -37,14 +37,29 @@ #define GPIO_SSUS_38_PAD 50 #define GPIO_SSUS_39_PAD 58 +static inline void disable_internal_pull(int pad) +{ + const int pull_mask = ~(0xf << 7); + write32(ssus_pconf0(pad), read32(ssus_pconf0(pad)) & pull_mask); +} + static void *get_spd_pointer(char *spd_file_content, int total_spds) { int ram_id = 0; + /* The ram_id[2:0] pullups on rambi are too large for the default 20K + * pulldown on the pad. Therefore, disable the internal pull resistor to + * read high values correctly. */ + disable_internal_pull(GPIO_SSUS_37_PAD); + disable_internal_pull(GPIO_SSUS_38_PAD); + disable_internal_pull(GPIO_SSUS_39_PAD); + ram_id |= (ssus_get_gpio(GPIO_SSUS_37_PAD) << 0); ram_id |= (ssus_get_gpio(GPIO_SSUS_38_PAD) << 1); ram_id |= (ssus_get_gpio(GPIO_SSUS_39_PAD) << 2); + printk(BIOS_DEBUG, "ram_id=%d, total_spds: %d\n", ram_id, total_spds); + if (ram_id >= total_spds) return NULL; -- cgit v1.2.3