Re: [PATCH 2/2] ACPI / scan: Fix enumeration for special UART devices

[Sebastian Reichel <sebastian.reichel@collabora.co.uk>]

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Hi,

On Sat, Oct 07, 2017 at 05:19:34PM +0200, Johan Hovold wrote:
> On Wed, Oct 04, 2017 at 10:51:30AM +0200, Frédéric Danis wrote:
> > UART devices is expected to be enumerated by SerDev subsystem.
> > 
> > During ACPI scan, serial devices behind SPI, I2C or UART buses are not
> > enumerated, allowing them to be enumerated by their respective parents.
> > 
> > Rename *spi_i2c_slave* to *serial_bus_slave* as this will be used for serial
> > devices on serial buses (SPI, I2C or UART).
> > 
> > On Macs an empty ResourceTemplate is returned for uart slaves.
> > Instead the device properties "baud", "parity", "dataBits", "stopBits" are
> > provided. Add a check for "baud" in acpi_is_serial_bus_slave().
> > 
> > Signed-off-by: Frédéric Danis <frederic.danis.oss@gmail.com>
> 
> So just to reiterate what I just mentioned in a comment to one of Hans's
> hci_bcm patches:
> 
> This one would silently break PM for such devices on any system which
> does not have serdev enabled (as the corresponding platform devices
> would no longer be registered). And with serdev enabled, hciattach
> (btattach) would start failing as the tty device would no longer be
> registered (but I assume everyone is aware of that, and fine with it, by
> now).
> 
> Perhaps the hci_bcm driver should start depending on
> SERIAL_DEV_CTRL_TTYPORT when ACPI is enabled?

ACPI and DT both need SERIAL_DEV_CTRL_TTYPORT to work properly,
since SERIAL_DEV_CTRL_TTYPORT is the only controller implemented
for serdev. If any other controller is implemented that one could
also be used.

I wonder if we should just hide SERIAL_DEV_CTRL_TTYPORT and enable
it together with SERDEV. I suspect that we won't see any other
controller (it would be a UART device, that is not registered as
tty device) in the next few years and the extra option seems to
confuse people.

-- Sebastian

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