On Sun, 2018-04-22 at 11:34 +0200, Rafael J. Wysocki wrote:
> On Fri, Apr 20, 2018 at 5:29 AM, Mark Salter <msalter@xxxxxxxxxx> wrote:
> > Commit e361d1f85855 ("ACPI / scan: Fix enumeration for special UART
> > devices") caused a regression with some X-Gene based platforms (Mustang
> > and M400) with invalid DSDT.
>
> I'm not convinced that making changes to the core ACPI device
> enumeration code in order to cover up for firmware bugs is the right
> approach.
It is unfortunate but the firmware bug predates the change which uncovered
it, so previously working systems no longer work.
>
> > The DSDT makes it appear that the UART
> > device is also a slave device attached to itself. With the above commit
> > the UART won't be enumerated by ACPI scan (slave serial devices shouldn't
> > be). So check for X-Gene UART device and skip slace device check on it.
> >
> > Signed-off-by: Mark Salter <msalter@xxxxxxxxxx>
> > ---
> > drivers/acpi/scan.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > index cc234e6a6297..1dcdd0122862 100644
> > --- a/drivers/acpi/scan.c
> > +++ b/drivers/acpi/scan.c
> > @@ -1551,6 +1551,14 @@ static bool acpi_device_enumeration_by_parent(struct acpi_device *device)
> > fwnode_property_present(&device->fwnode, "baud")))
> > return true;
> >
> > + /*
> > + * Firmware on some arm64 X-Gene platforms will make the UART
> > + * device appear as both a UART and a slave of that UART. Just
> > + * bail out here for X-Gene UARTs.
> > + */
> > + if (!strcmp(acpi_device_hid(device), "APMC0D08"))
> > + return false;
>
> Is the device ID never to be used outside of the broken configurations?
>
> Even if that's the plan, how are you going to guarantee that anyway?
The device ID will always be used for X-Gene UARTs. Whether the DSDT is
broken or not wouldn't matter because the end result would be the same
(the UART being treated as master rather than a serial bus slave).
The broken firmware looks like this:
Device (URT0)
{
Name (_HID, "APMC0D08") // _HID: Hardware ID
...
Name (_CRS, ResourceTemplate () // _CRS: Current Resource Settings
{
Memory32Fixed (ReadWrite,
0x1C020000, // Address Base
0x00000100, // Address Length
)
UartSerialBusV2 (0x0001C200, DataBitsEight, StopBitsOne,
0x00, LittleEndian, ParityTypeNone, FlowControlNone,
0x0010, 0x0010, "URT0",
0x00, ResourceConsumer, , Exclusive,
)
Interrupt (ResourceConsumer, Level, ActiveHigh, Exclusive, ,, )
{
0x0000006D,
}
})
...
}
So "URT0" has a UartSerialBusV2 resource which references itself as the bus master.
>
> > +
> > INIT_LIST_HEAD(&resource_list);
> > acpi_dev_get_resources(device, &resource_list,
> > acpi_check_serial_bus_slave,
> > --
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