From 4f5936b45652cea97f964678c93083b0a4f2e478 Mon Sep 17 00:00:00 2001 From: Raul E Rangel Date: Thu, 11 Jun 2020 16:27:49 -0600 Subject: soc/amd/picasso: Explicitly disable legacy UART The legacy UARTs are supposed to default to off according to the documentation (PPR for AMD Family 17h Model 18h). But legacy UART Range_0 is enabled after reset. The PSP might be enabling it or the documentation might be wrong. Having it enabled causes problems though. We have ACPI nodes defining MMIO UARTs, and the kernel also probes for legacy UARTs. This results in two drivers accessing the same device, one via MMIO and one via IO. I suspect this was the cause of the garbage serial output. Before the change you would see the following in the console: [ 0.741108] serial8250: ttyS3 at I/O 0x2e8 (irq = 3, base_baud = 115200) is a 16550A After this change, we no longer see it. BUG=b:152079780, b:157858890 TEST=Boot trembyle and make sure serial is still working. Signed-off-by: Raul E Rangel Change-Id: I9d837e449b961dbb55d1301d2107838e26b3f892 Reviewed-on: https://review.coreboot.org/c/coreboot/+/42323 Tested-by: build bot (Jenkins) Reviewed-by: Aaron Durbin Reviewed-by: Furquan Shaikh Reviewed-by: Marshall Dawson --- src/soc/amd/picasso/southbridge.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'src/soc/amd/picasso/southbridge.c') diff --git a/src/soc/amd/picasso/southbridge.c b/src/soc/amd/picasso/southbridge.c index a18f5a37bd..d2904d894b 100644 --- a/src/soc/amd/picasso/southbridge.c +++ b/src/soc/amd/picasso/southbridge.c @@ -226,6 +226,13 @@ void fch_pre_init(void) sb_enable_legacy_io(); enable_aoac_devices(); sb_reset_i2c_slaves(); + + /* + * On reset Range_0 defaults to enabled. We want to start with a clean + * slate to not have things unexpectedly enabled. + */ + clear_uart_legacy_config(); + if (CONFIG(PICASSO_UART)) set_uart_config(CONFIG_UART_FOR_CONSOLE); } -- cgit v1.2.3