On Wed, Feb 09, 2022 at 11:40:42PM PST, Greg Kroah-Hartman wrote:
On Wed, Feb 09, 2022 at 12:34:14PM -0800, Zev Weiss wrote: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. Signed-off-by: Zev Weiss <zev@xxxxxxxxxxxxxxxxx> Tested-by: Konstantin Aladyshev <aladyshev22@xxxxxxxxx>Do we need a "Fixes:" tag here as well?
I was wondering the same -- I left it out because it didn't seem like it was strictly a bug in the earlier commit that's really being fixed per se, but perhaps that's an overly pedantic distinction. I can certainly add it if you'd prefer.
--- 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..cd11748833e6 100644 --- a/include/uapi/linux/serial_core.h +++ b/include/uapi/linux/serial_core.h @@ -274,4 +274,7 @@ /* Freescale LINFlexD UART */ #define PORT_LINFLEXUART 122 +/* ASPEED AST2x00 virtual UART */ +#define PORT_ASPEED_VUART 123Why does this value have to be in a uapi header file? What userspace tool is going to need this?
I only put it there because that was where all the other port type constants were defined, and wondered the same thing about the lot of them. Is there a userspace tool that makes use of any of these?
Zev
