From: Zev Weiss zev@bewilderbeest.net
[ Upstream commit a603ca60cebff8589882427a67f870ed946b3fc8 ]
Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to set up register mapping") fixed a bug that had, as a side-effect, prevented the 8250_aspeed_vuart driver from enabling the VUART's FIFOs. However, fixing that (and hence enabling the FIFOs) has in turn revealed what appears to be a hardware bug in the ASPEED VUART in which the host-side THRE bit doesn't get if the BMC-side receive FIFO trigger level is set to anything but one byte. This causes problems for polled-mode writes from the host -- for example, Linux kernel console writes proceed at a glacial pace (less than 100 bytes per second) because the write path waits for a 10ms timeout to expire after every character instead of being able to continue on to the next character upon seeing THRE asserted. (GRUB behaves similarly.)
As a workaround, introduce a new port type for the ASPEED VUART that's identical to PORT_16550A as it had previously been using, but with UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to one byte, which (experimentally) seems to avoid the problematic THRE behavior.
Fixes: 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to set up register mapping") Tested-by: Konstantin Aladyshev aladyshev22@gmail.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Zev Weiss zev@bewilderbeest.net Link: https://lore.kernel.org/r/20220211004203.14915-1-zev@bewilderbeest.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/8250/8250_aspeed_vuart.c | 2 +- drivers/tty/serial/8250/8250_port.c | 8 ++++++++ include/uapi/linux/serial_core.h | 3 +++ 3 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c index 2350fb3bb5e4..c2cecc6f47db 100644 --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c @@ -487,7 +487,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) port.port.irq = irq_of_parse_and_map(np, 0); port.port.handle_irq = aspeed_vuart_handle_irq; port.port.iotype = UPIO_MEM; - port.port.type = PORT_16550A; + port.port.type = PORT_ASPEED_VUART; port.port.uartclk = clk; port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST; diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 3b12bfc1ed67..973870ebff69 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -307,6 +307,14 @@ static const struct serial8250_config uart_config[] = { .rxtrig_bytes = {1, 32, 64, 112}, .flags = UART_CAP_FIFO | UART_CAP_SLEEP, }, + [PORT_ASPEED_VUART] = { + .name = "ASPEED VUART", + .fifo_size = 16, + .tx_loadsz = 16, + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00, + .rxtrig_bytes = {1, 4, 8, 14}, + .flags = UART_CAP_FIFO, + }, };
/* Uart divisor latch read */ diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h index c4042dcfdc0c..8885e69178bd 100644 --- a/include/uapi/linux/serial_core.h +++ b/include/uapi/linux/serial_core.h @@ -68,6 +68,9 @@ /* NVIDIA Tegra Combined UART */ #define PORT_TEGRA_TCU 41
+/* ASPEED AST2x00 virtual UART */ +#define PORT_ASPEED_VUART 42 + /* Intel EG20 */ #define PORT_PCH_8LINE 44 #define PORT_PCH_2LINE 45