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Zev Weiss a603ca60ce serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type 
Commit 54da3e381c ("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: 54da3e381c ("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>
 		2022-02-21 19:48:34 +01:00
..
asm-generic mm/mempolicy: wire up syscall set_mempolicy_home_node 2022-01-15 16:30:30 +02:00
drm Merge tag 'amd-drm-next-5.17-2021-12-16' of https://gitlab.freedesktop.org/agd5f/linux into drm-next 2021-12-23 11:55:28 +10:00
linux serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type 2022-02-21 19:48:34 +01:00
misc habanalabs: change wait_for_interrupt implementation 2021-12-26 08:59:09 +02:00
mtd
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rdma RDMA v5.17 merge window pull request 2022-01-13 11:09:11 -08:00
scsi scsi: fc: Add EDC ELS definition 2021-08-24 22:56:33 -04:00
sound ASoC: Fixes for v5.17 2022-02-01 16:52:54 +01:00
video
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xen Improve docs for IOCTL_GNTDEV_MAP_GRANT_REF 2022-02-03 08:23:32 +01:00
Kbuild
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