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| author | Zev Weiss <zev@bewilderbeest.net> | 2022-02-11 01:42:03 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-02-21 19:48:34 +0100 |
| commit | a603ca60cebff8589882427a67f870ed946b3fc8 (patch) | |
| tree | 5877969158e785d7d1cd4a19211158bb05dbdea6 /include/uapi | |
| parent | serial: 8250_mid: Remove unneeded test for ->setup() presence (diff) | |
| download | linux-a603ca60cebff8589882427a67f870ed946b3fc8.tar.xz linux-a603ca60cebff8589882427a67f870ed946b3fc8.zip | |
serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type
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>
Diffstat (limited to 'include/uapi')
| -rw-r--r-- | include/uapi/linux/serial_core.h | 3 |
1 files changed, 3 insertions, 0 deletions
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 |