[U-Boot] [PATCH 1/3] dm: serial: Do not panic if no serial ports are found

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 06-07-15 18:39, Simon Glass wrote:
> Hi Hans,
>
> On 5 July 2015 at 12:56, Hans de Goede <hdegoede@redhat.com> wrote:
>> Some boards simply do not have any serial ports. Also no one will see the
>> panic message as there is no where to print it if no serial port is found
>> (and other stdout options are not yet set up at this point).
>>
>
> It is visible (or will be when some patches land) if you have a debug
> UART set up.

Ok.

>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>   drivers/serial/serial-uclass.c | 8 +++-----
>>   1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
>> index 815fec3..f036499 100644
>> --- a/drivers/serial/serial-uclass.c
>> +++ b/drivers/serial/serial-uclass.c
>> @@ -27,7 +27,7 @@ static const unsigned long baudrate_table[] = CONFIG_SYS_BAUDRATE_TABLE;
>>   #error "Serial is required before relocation - define CONFIG_SYS_MALLOC_F_LEN to make this work"
>>   #endif
>>
>> -static void serial_find_console_or_panic(void)
>> +static void serial_find_console(void)
>>   {
>>          struct udevice *dev;
>>          int node;
>> @@ -77,14 +77,12 @@ static void serial_find_console_or_panic(void)
>>                  }
>>   #undef INDEX
>>          }
>> -
>> -       panic_str("No serial driver found");
>>   }
>>
>>   /* Called prior to relocation */
>>   int serial_init(void)
>>   {
>> -       serial_find_console_or_panic();
>> +       serial_find_console();
>>          gd->flags |= GD_FLG_SERIAL_READY;
>>
>>          return 0;
>> @@ -93,7 +91,7 @@ int serial_init(void)
>>   /* Called after relocation */
>>   void serial_initialize(void)
>>   {
>> -       serial_find_console_or_panic();
>> +       serial_find_console();
>>   }
>>
>>   static void _serial_putc(struct udevice *dev, char ch)
>
> How is this handled before driver model?

It was not, the boards involved all use the A13 SoC which is the
same die as the A10s but then in a different (cheaper) package
with way less pins. As such uart0 is not routed to the outside
on the A13. When not setting CONFIG_DM_SERIAL we are simply using
uart0 as serial console, and that ends at the bonding pads at the
edge of the die. doing things that way is not really useful,
but there is a serial console and u-boot is happy.

In the non devicetree world this sort of was a natural hack, we
simply left CONSOLE_INDEX undefined for these boards, which causes
it to default to 1 / uart0 and things just work. I had never given
this much thought until moving to devicetree.

As you can hopefully understand I do not want to do the samething
with DM_SERIAL builds as that would require hacking up the dts
to add a node for hardware which is effectively disabled for the
A13 package of the sun5i die.

 > It is possible to mark a
> device disabled in device tree - perhaps we should have a way to see
> that the console is present (i.e. there is an alias) but it is
> disabled?

That seems rather ugly, I really do not want to add an alias to
a non enabled device, that just feels wrong on all levels.

> Normally a serial console is required, so I'd like to preserve this
> behaviour for most boards.

Ok, I actually expected as much, this was actually my second solution
for the problem at hand, but as it was the simplest solution I decided
to submit this version first. My first / original solution is to add a
CONFIG_DM_SERIAL_NO_PANIC Kconfig option which can then be set on boards
which have no serial port.

Or probably better a CONFIG_DM_SERIAL_NO_SERIAL_CONSOLE option ?

This option would disable the panic / disable probing all together while
we would keep using DM_SERIAL on these boards, because:

1) Consistency I really want to use DM_FOO everywhere for sunxi
2) The non dm serial code cannot handle not having a serial port either,
    and fixing it looks like it is going to be a bit harder (from a quick
    glance).

Regards,

Hans