drivers: PL011: add ARM SBSA Generic UART support
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Cover letter [PATCH 00/10] drivers: PL011: add ARM SBSA Generic UART support
Hi Arnd,
Quoted 9 lines · Arnd Bergmann
Quoted 7 lines · On Friday 16 January 2015 17:22:56 Andre Przywara wrote:
The ARM Server Base System Architecture[1] document describes a generic UART which is a subset of the PL011 UART.
It lacks DMA support, baud rate control and modem status line control, among other things.
The idea is to move the UART initialization and setup into the firmware (which does this job today already) and let the kernel just use the UART for sending and receiving characters.
Quoted 4 lines
Given that all other approaches that have been tried have failed, this seems like the best way forward. I don't know enough about the driver to do a detailed review, but all patches looked good to me as far as I could tell.
Thanks for looking at them!
Quoted 3 lines
One question: How does the name space and minor number allocation work if you have both sbsa-uart and real pl011 in the same system? Do they share the ttyAMA name space without collisions?
Yes, that works. Both parts use the same pl011_probe_dt_alias() routine to do the numbering.
For testing I specified the second and fourth port as SBSA in the DT, leaving the first and third as PL011. This is what you get then:
...
Serial: AMBA PL011 UART driver
uart-pl011 1c090000.uart: ttyAMA0 at MMIO 0x1c090000 (irq = 15, base_baud = 0) is a PL011 rev2
...
uart-pl011 1c0b0000.uart: ttyAMA2 at MMIO 0x1c0b0000 (irq = 17, base_baud = 0) is a PL011 rev2
....
sbsa-uart 1c0a0000.uart: ttyAMA1 at MMIO 0x1c0a0000 (irq = 16, base_baud = 0) is a SBSA
sbsa-uart 1c0c0000.uart: ttyAMA3 at MMIO 0x1c0c0000 (irq = 18, base_baud = 0) is a SBSA
Cheers,
Andre.