[PATCH v2] serial: 8250_dw: Improve unwritable LCR workaround

On Tue, Nov 26, 2013 at 10:36 AM, Ezequiel Garcia
[off-list ref] wrote:

Since v3.13-rc1, this commit seems to have introduced some oddities on
some of our boards. See this log snippet:

Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
????R?console [ttyS0] enabled
console [ttyS0] enabled
bootconsole [earlycon0] disabled
bootconsole [earlycon0] disabled
dw-apb-uart d0012100.serial: Couldn't set LCR to 191
dw-apb-uart d0012100.serial: Couldn't set LCR to 191
dw-apb-uart d0012100.serial: Couldn't set LCR to 224
dw-apb-uart d0012100.serial: Couldn't set LCR to 224
d0012100.serial: ttyS1 at MMIO 0xd0012100 (irq = 18, base_baud = 15625000) is a 16550A

This behavior appear in at least Armada 370 and Armada XP boxes.

I confirm reverting this commit fixes the issue and things get back to normal.
Here's the complete kernel log: sprunge.us/gMdL

Ideas?

Hi Ezequiel,

An external device may be keeping the UART busy and preventing LCR
from being written.

What device is attached to ttyS1?  Also, do you know the version of
the Synopsys IP?

If built with ADDITIONAL_FEATURES=YES, the version can be read from
the hardware:

# busybox devmem 0xd00121f8 32

-Tim