Commit a603ca60 authored by Zev Weiss's avatar Zev Weiss Committed by Greg Kroah-Hartman
Browse files

serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type 



Commit 54da3e38 ("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: 54da3e38 ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to set up register mapping")
Tested-by: default avatarKonstantin Aladyshev <aladyshev22@gmail.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarZev Weiss <zev@bewilderbeest.net>
Link: https://lore.kernel.org/r/20220211004203.14915-1-zev@bewilderbeest.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 324facd1

drivers/tty/serial/8250/8250_aspeed_vuart.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

drivers/tty/serial/8250/8250_port.c

+8 −0
Original line number Diff line number Diff line
@@ -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 */

include/uapi/linux/serial_core.h

+3 −0
Original line number Diff line number Diff line
@@ -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