On Wed, Nov 12, 2014 at 1:04 AM, Arnd Bergmann [off-list ref] wrote:

On Wednesday 12 November 2014 00:46:30 Kevin Cernekee wrote:

quoted

Remove the platform dependency in Kconfig and add an appropriate
compatible string.  Note that BCM7401 has one 16550A-compatible UART
in the UPG uart_clk domain, and two proprietary UARTs in the 27 MHz
clock domain.  This driver handles the former one.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>

Can you explain why you are using the PXA serial driver instead of the
8250 driver, if this is 16550A compatible? I don't know the history
why PXA is using a separate driver.

I wasn't able to get serial8250 to work in any situation where another
driver tried to claim "ttyS"/4/64.

serial8250 calls uart_add_one_port() in its module_init function, even
if the system doesn't have any ports.  Setting nr_uarts
(CONFIG_SERIAL_8250_RUNTIME_UARTS) to 0 doesn't help because
serial8250_find_match_or_unused() will just return NULL.

I guess I could try to rework that logic but several cases would need
to be retested, going back to PCs with ISA buses and PCI add-in cards.
And the differences may be visible to userspace.

The PXA driver seemed like a much cleaner starting point, even if it
was intended for a different SoC.