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

[Simon Glass]

+Masahiro

Hi Hans,

On 8 July 2015 at 05:56, Hans de Goede <hdegoede at redhat.com> wrote:
> Hi Simon,
>
>
> On 07-07-15 09:00, Hans de Goede wrote:
>>
>> Hi,
>>
>> On 06-07-15 18:39, Simon Glass wrote:
>>>
>>> Hi Hans,
>>>
>>> On 5 July 2015 at 12:56, Hans de Goede <hdegoede at 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 at 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).
>
>
> You probably just have not gotten around to this yet, but in case it is
> not clear, the above solution (adding a CONFIG_DM_SERIAL_NO_SERIAL_CONSOLE
> Kconfig option) is a suggestion on how to fix. I'll happily implement this
> if people like it, but atm I'm waiting for feedback on the suggestion.
>

I've been thinking about it. Perhaps an option to allow U-Boot to run
without a console is best. But instead of CONFIG_DM_SERIAL_NO_PANIC,
perhaps we could have CONFIG_REQUIRE_CONSOLE which is normally y. I
don't think this has anything to do with driver model and we should
try to use CONFIG_DM... only when the old and new code paths coexist.

I added Masahiro also in case he has ideas.

> Regards,
>
> Hans
>
> p.s.
>
> I'm on vacation from July 11th - July 19th, so if I'm quiet that is why :)

Have fun!

Regards,
Simon