Re: [PATCH] ARM64: tegra: Add support for Google Pixel C

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 07/01/16 14:11, Arnd Bergmann wrote:
> On Thursday 07 January 2016 13:19:44 Jon Hunter wrote:
>>
>> Adding Arnd.
>>
>> Hmmm ... well apparently stdout-path does not work for tegra and in
>> order to make this work I had to do the following ...
>>
>>
>> [PATCH] serial: 8250: of: Add earlycon support for Tegra
>>
>> Currently, early console support only works for Tegra when the serial
>> port information is passed via the earlycon boot parameter. If the
>> serial port information is specified via device-tree using the
>> "stdout-path" then the early console does not work because:
>>
>> 1. The tegra serial ports compatibility parameter does not match any
>>    of the supported serial drivers for early console.
>> 2. The of_setup_earlycon() function assumes that serial port registers
>>    are byte aligned and for tegra they are 32-bit aligned.
>>
>> Add an early console setup function for tegra so that the early console
>> can be specified via the device-tree "stdout-path" variable.
>>
>> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>> ---
>>  drivers/tty/serial/8250/8250_of.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
>> index 33021c1f7d55..98adf83e83c2 100644
>> --- a/drivers/tty/serial/8250/8250_of.c
>> +++ b/drivers/tty/serial/8250/8250_of.c
>> @@ -44,6 +44,16 @@ void tegra_serial_handle_break(struct uart_port *p)
>>                 udelay(1);
>>         } while (1);
>>  }
>> +
>> +int __init tegra_earlycon_setup(struct earlycon_device *device,
>> +                               const char *options)
>> +{
>> +       device->port.iotype = UPIO_MEM32;
>> +       device->port.regshift = 2;
>> +
>> +       return early_serial8250_setup(device, options);
>> +}
>> +OF_EARLYCON_DECLARE(tegra20_uart, "nvidia,tegra20-uart", tegra_earlycon_setup);
>>  #else
>>  static inline void tegra_serial_handle_break(struct uart_port *port)
>>  {
>>
>>
>> Arnd, does the above look ok, or should there be a generic
>> early_serial8250x32_setup() somewhere?
> 
> I think it would be better to put it into 8250_early.c rather than 
> 8250_of.c, as there are already some other definitions in there,
> and the #ifdef CONFIG_TEGRA in 8250_of.c is for some other workaround.

Ok so something like this ...

diff --git a/drivers/tty/serial/8250/8250_early.c
b/drivers/tty/serial/8250/8250_early.c
index af62131af21e..4ce6e2b57534 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -141,7 +141,18 @@ int __init early_serial8250_setup(struct
earlycon_device *device,
        device->con->write = early_serial8250_write;
        return 0;
 }
+
+int __init early_serial8250_mem32_setup(struct earlycon_device *device,
+                                       const char *options)
+{
+       device->port.iotype = UPIO_MEM32;
+       device->port.regshift = 2;
+
+       return early_serial8250_setup(device, options);
+}
 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 EARLYCON_DECLARE(uart, early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
+OF_EARLYCON_DECLARE(tegra20_uart, "nvidia,tegra20-uart",
+                   early_serial8250_mem32_setup);

> Would it be possible to handle the "reg-io-width" parsing in
> early_serial8250_setup instead of keying it off the string?

Good point. I spent a bit of time looking at this, but I cannot see an
easy way to do this unless we check for "reg-io-width" and "reg-shift"
in early_init_dt_scan_chosen_serial() and pass to of_setup_earlycon(),
however, I am guessing that this would not be ideal as this would happen
for non-8250 devices. May be that would be ok, but I am not sure.

Cheers
Jon