ARM64: tegra: Add support for Google Pixel C

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@nvidia.com>
>> ---
>>  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 ...

+                   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
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On Thu, Jan 7, 2016 at 10:53 AM, Jon Hunter <jonathanh@nvidia.com> wrote:
>
> On 07/01/16 14:11, Arnd Bergmann wrote:
>> On Thursday 07 January 2016 13:19:44 Jon Hunter wrote:

[...]

> 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.

There's been one attempt[1] already. It had a few issues easily
solved, but I haven't seen a follow-up.

Rob

[1] https://lkml.org/lkml/2015/11/30/513
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On 07/01/16 17:20, Rob Herring wrote:
> On Thu, Jan 7, 2016 at 10:53 AM, Jon Hunter <jonathanh@nvidia.com> wrote:
>>
>> On 07/01/16 14:11, Arnd Bergmann wrote:
>>> On Thursday 07 January 2016 13:19:44 Jon Hunter wrote:
> 
> [...]
> 
>> 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.
> 
> There's been one attempt[1] already. It had a few issues easily
> solved, but I haven't seen a follow-up.

Thanks. Adding Paul.

Paul, are you planning a follow-up to your patch? Otherwise, I am happy
to have crack at it. Don't we also need to read the "reg-shift"?

Cheers
Jon


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