Dear Lei Wen,
In message AANLkTi=BbS7wzcbsH26Hb0y_GVXzHtEQspoVZkKn1PMU@mail.gmail.com you wrote:
Can you please explain on what board, and with which tool chain, you see any problems?
I test on Marvell pxa955 (MG1) board, with android 4.4.0 toolchain. The pxa955's ns16550 register's IER has nine bits. The 8th bit is HSE, which means the high speed mode. It seems something wrong there, if access the ier by byte, the 8th bit would be 1 at the beginning, and would be cleared by the following set value in the ns16550 driver, which cause problem on that board, for the baudrate would be dysfunction.
This makes no sense to me. I have never seen any 9 bit registers in any processor I ever encountered in real life.
Registers are typically 8, 16, 32 or 64 bit.
If your register holds 9 data bits, then it is most probably a 16 or 32 bit wide register.
Also, in this case the serial controller is probably not NS16550 compatible, because AFAICT the NS16550 uses only 8 bit wide registers.
Further, it is not clear to me why there is a Mervell specific version of the NS16550 driver (board/Marvell/common/ns16550.*).
Best regards,
Wolfgang Denk