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 Sun, Oct 08, 2017 at 10:51:52AM +0200, Marcel Holtmann wrote:
> Hi Sebastian,
> 
> >>> 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.
> 
> I wonder if we should just default SERIAL_DEV_CTRL_TTYPORT=y when
> DT or ACPI is enabled. Then no driver would have to select or
> depend on it.

This is not related to DT/ACPI. SERIAL_DEV_CTRL_TTYPORT is a serdev
controller driver, that registers serdev controller devices for each
tty. It will also be used by clients, that are registered via board
code.

-- Sebastian

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