[U-Boot] [PATCH] serial: 16550: Add JZ47xx support

[Marek Vasut]

On 05/26/2016 06:48 PM, Simon Glass wrote:
> Hi Marek,
> 
> On 26 May 2016 at 10:47, Marek Vasut <marex at denx.de> wrote:
>> On 05/26/2016 06:44 PM, Simon Glass wrote:
>>> Hi Marek,
>>>
>>> On 26 May 2016 at 10:34, Marek Vasut <marex at denx.de> wrote:
>>>> On 05/26/2016 03:29 PM, Simon Glass wrote:
>>>>> Hi Marek,
>>>>>
>>>>> On 25 May 2016 at 16:35, Marek Vasut <marex at denx.de> wrote:
>>>>>> On 05/26/2016 12:31 AM, Daniel Schwierzeck wrote:
>>>>>>>
>>>>>>>
>>>>>>> Am 26.05.2016 um 00:21 schrieb Marek Vasut:
>>>>>>>> On 05/26/2016 12:17 AM, Daniel Schwierzeck wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Am 25.05.2016 um 02:19 schrieb Marek Vasut:
>>>>>>>>>> The Ingenic JZ47xx requires special bit (UART_EN) set in FCR register
>>>>>>>>>> in order to work at all. Add this special case handling into the driver.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Marek Vasut <marex at denx.de>
>>>>>>>>>> Cc: Tom Rini <trini at konsulko.com>
>>>>>>>>>> Cc: Simon Glass <sjg at chromium.org>
>>>>>>>>>> Cc: Daniel Schwierzeck <daniel.schwierzeck at gmail.com>
>>>>>>>>>> Cc: Paul Burton <paul.burton at imgtec.com>
>>>>>>>>>> ---
>>>>>>>>>>  drivers/serial/ns16550.c | 8 ++++++++
>>>>>>>>>>  1 file changed, 8 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
>>>>>>>>>> index 30ba0aa..1323881 100644
>>>>>>>>>> --- a/drivers/serial/ns16550.c
>>>>>>>>>> +++ b/drivers/serial/ns16550.c
>>>>>>>>>> @@ -50,6 +50,14 @@ DECLARE_GLOBAL_DATA_PTR;
>>>>>>>>>>  #endif
>>>>>>>>>>  #endif
>>>>>>>>>>
>>>>>>>>>> +#ifdef CONFIG_ARCH_JZ47XX
>>>>>>>>>> +#undef UART_FCRVAL
>>>>>>>>>> +/* Ingenic JZ47xx SoCs require that a 'UART Module Enable' bit be set */
>>>>>>>>>> +#define UART_FCR_UME              0x10
>>>>>>>>>> +#define UART_FCRVAL (UART_FCR_FIFO_EN | UART_FCR_RXSR |   \
>>>>>>>>>> +               UART_FCR_TXSR | UART_FCR_UME)
>>>>>>>>>> +#endif
>>>>>>>>>
>>>>>>>>> I think this could be added as DT property
>>>>>>>>
>>>>>>>> Not for SPL, which has 14 kiB size limit and it is itching to overflow.
>>>>>>>> I am literally counting bytes in the SPL and removing slop from
>>>>>>>> structures to make it fit, just barely. With the USB loader, I can
>>>>>>>> brutalize the SPL into having extremely rudimentary UART support now
>>>>>>>> (like printch() being the most advanced output mechanism, but you can
>>>>>>>> only use it three times, otherwise the code won't fit and the board is
>>>>>>>> eaten by demons) and this is where this patch comes into play.
>>>>>>>>
>>>>>>>> So yes, for full u-boot, this _should_ be part of DT. For SPL, please apply.
>>>>>>>>
>>>>>>>
>>>>>>> ok, but wouldn't it be better to introduce an option like
>>>>>>> CONFIG_SYS_NS16550_UME instead of using the SoC-specific
>>>>>>> CONFIG_ARCH_JZ47XX. This driver is messed up enough ;)
>>>>>>
>>>>>> I was undecided between this (like the IER) and adding new ifdef (like
>>>>>> SOC_KEYSTONE). Whichever way is fine with me. Yeah, the driver is
>>>>>> repugnant for sure.
>>>>>>
>>>>>>>>>> +
>>>>>>>>>>  #ifndef CONFIG_SYS_NS16550_IER
>>>>>>>>>>  #define CONFIG_SYS_NS16550_IER  0x00
>>>>>>>>>>  #endif /* CONFIG_SYS_NS16550_IER */
>>>>>>>>>>
>>>>>
>>>>> That way seems better to me. You should be able to add your UME flag
>>>>> as a Kconfig for this driver, in drivers/serial/Kconfig, which
>>>>> defaults to 0. It would be good to keep out board-specific stuff from
>>>>> this file, as you did with OMAP1510.
>>>>
>>>> I'm not really sure I want to expose the CONFIG_SYS_NS16550_FCR override
>>>> via Kconfig. The extra bits should be set via DT props
>>>> unless there is some really good reason why that cannot be done
>>>> (like size limitation in SPL or DT not available).
>>>>
>>>> I tried these approaches:
>>>> 1) Add Kconfig option for CONFIG_SYS_NS16550_FCR , where you
>>>>    set specific byte value. This makes it hard to figure out
>>>>    which bits are set in the FCR just by looking at the value.
>>>> 2) Add Kconfig option selected if ARCH_JZ47XX is selected and
>>>>    use that in the driver to add the extra UME bit.
>>>> 3) Define CONFIG_SYS_NS16550_FCR in include/configs/board.h
>>>>    using the macros from ns16550.h . This makes it obvious
>>>>    which bits are set.
>>>>
>>>> I am undecided between 2 and 3, but inclined to go with 3.
>>>> What do you think ?
>>>
>>> How about making your feature an option, like CONFIG_SYS_NS16550_UEN,
>>> which defaults to 0, but in your case is 0x10. You can OR it into the
>>> value.
>>
>> That's quite close to 1) , but then what if someone comes and wants to
>> remove some bits from the FCR instead of adding some?
> 
> Seems like speculative complexity to me - let's worry about it when it happens!

Maybe this is not even worth the effort and I should just ignore serial
support in SPL and only go with serial support in full u-boot, where I
can configure the FCR from DT. Then we avoid all this complex stuff.


-- 
Best regards,
Marek Vasut