From 0ec058ece2f933aed66b76bd5cb9b5e6764853c3 Mon Sep 17 00:00:00 2001 From: Ayan Kumar Halder Date: Tue, 5 Dec 2023 12:35:34 +0000 Subject: [PATCH] tty: hvc: dcc: Check for TXfull condition while setting up early console Refer ARM DDI 0487I.a ID081822, D17.3.8, DBGDTRTX_EL0, "If TXfull is set to 1, set DTRRX and DTRTX to UNKNOWN" Thus one should always check for TXfull condition before hvc can be used as an early console. This is similar to what is being done today in hvc_dcc_console_init() and hvc_dcc_init(). The count 0x4000000 has been obtained from uboot (v2024.01-rc3) drivers/serial/arm_dcc.c "TIMEOUT_COUNT". It reads the dcc status and waits for 0x4000000 times for the TX Fifo to be available before returning an error. Thus, it will prevent DCC to be used as early console. Signed-off-by: Ayan Kumar Halder Link: https://lore.kernel.org/r/20231205123534.3376883-1-ayan.kumar.halder@amd.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/hvc/hvc_dcc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c index 1751108cf763e..136381bec7cd7 100644 --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -47,6 +47,14 @@ static void dcc_early_write(struct console *con, const char *s, unsigned n) static int __init dcc_early_console_setup(struct earlycon_device *device, const char *opt) { + unsigned int count = 0x4000000; + + while (--count && (__dcc_getstatus() & DCC_STATUS_TX)) + cpu_relax(); + + if (__dcc_getstatus() & DCC_STATUS_TX) + return -ENODEV; + device->con->write = dcc_early_write; return 0; -- 2.30.2