[U-Boot] [PATCH] arm: socfpga: make debug uart work on socfpga_gen5

[Marek Vasut]

On 1/8/19 1:06 PM, Simon Goldschmidt wrote:
> On Tue, Jan 8, 2019 at 12:20 PM Marek Vasut <marex at denx.de> wrote:
>>
>> On 1/8/19 7:41 AM, Simon Goldschmidt wrote:
>>> On Mon, Jan 7, 2019 at 11:58 PM Marek Vasut <marex at denx.de> wrote:
>>>>
>>>> On 1/7/19 10:01 PM, Simon Goldschmidt wrote:
>>>>> Am 07.01.2019 um 21:47 schrieb Marek Vasut:
>>>>>> On 1/7/19 9:33 PM, Simon Goldschmidt wrote:
>>>>>>> Am 07.01.2019 um 21:25 schrieb Marek Vasut:
>>>>>>>> On 1/7/19 9:24 PM, Simon Goldschmidt wrote:
>>>>>>>>> Am 07.01.2019 um 21:19 schrieb Marek Vasut:
>>>>>>>>>> On 1/7/19 8:36 PM, Simon Goldschmidt wrote:
>>>>>>>>>>> When debug UART is enabled on socfpga_gen5, the debug uart driver
>>>>>>>>>>> hangs
>>>>>>>>>>> in an endless loop because 'socfpga_bridges_reset' calls printf
>>>>>>>>>>> before
>>>>>>>>>>> the debug UART is initialized.
>>>>>>>>>>>
>>>>>>>>>>> After the generic fix for this in the UART driver did not work
>>>>>>>>>>> due to
>>>>>>>>>>> portability issues, let's just drop this printf statement when
>>>>>>>>>>> called
>>>>>>>>>>> from SPL with debug UART enabled.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>
>>>>>>>>>>
>>>>>>>>>> Can we have an un-portable fix which at least works on SoCFPGA ? :)
>>>>>>>>>
>>>>>>>>> This one worked on socfpga but broke rockchip:
>>>>>>>>>
>>>>>>>>> https://patchwork.ozlabs.org/patch/992553/
>>>>>>>>>
>>>>>>>>> However, the message below wasn't shown either with that patch
>>>>>>>>> applied.
>>>>>>>>> The code just runs too early to enable the UART.
>>>>>>>>>
>>>>>>>>> Do you want to keep the message (although I failed to see in which
>>>>>>>>> situation it can be printed) or do you just dislike the #ifdef thing?
>>>>>>>>
>>>>>>>> I'd like to keep the error message if possible. Is it possible ?
>>>>>>>
>>>>>>> I have *never* seen this message yet. I have failed to produce a
>>>>>>> situation where it is shown.
>>>>>>
>>>>>> I believe that.
>>>>>>
>>>>>>> This function ('socfpga_bridges_reset') is called 5 times throughout the
>>>>>>> code, but only *one* single time with 'reset=0' as argument (only with
>>>>>>> 0, the code in question is executed). And this is in SPL before
>>>>>>> initializing the console and even before the debug UART can be
>>>>>>> initialized.
>>>>>>>
>>>>>>> As I could see, the printf *is* executed on every boot (I saw the code
>>>>>>> hanging when enabling debug UART). However, when not booting from FPGA,
>>>>>>> it is just normal that the FPGA is not ready when running SPL. Why do
>>>>>>> you want an error message here anyway?
>>>>>>
>>>>>> I was under the impression this is an error message, but it might not be
>>>>>> so ? Maybe the wording is incorrect ?
>>>>>
>>>>> Now that I re-read it, "aborting" is incorrect, yes.
>>>>>
>>>>> So how should we proceed? This is an error message that can never be
>>>>> shown (like the code is now) but breaks debug UART.
>>>>>
>>>>> I'd say we can drop it altogether. It might only be interesint if (in
>>>>> the future) that code would get called from somewhere else (i.e. later,
>>>>> after console initialization).
>>>>>
>>>>> Re-reading spl_gen5.c, there are some 'debug' calls before the debug
>>>>> uart is initialized which probably would need to be removed as well, but
>>>>> that's a different story...
>>>>
>>>> How come those don't hang the system then ?
>>>
>>> I just haven't enabled debug output in spl_gen5.c, yet. I guess they would hang
>>> the system when enabling them.
>>>
>>> While it would be easy to remove these debug statements, to be future-proof
>>> it would of course make sense to make the debug UART robust against this.
>>>
>>> But given the problems with Rockchip ns16550, we would need a dedicated
>>> debug UART for socfpga to solve this. And that would probably mean code
>>> duplication.
>>
>> What is the problem with Rockchip ? I don't want various SoCs blocking
>> others.
> 
> I had sent a patch that does not wait for the TX fifo to hold more bytes if the
> baudrate prescaler is 0 (according to both the socfgpa and the rockchip docs,
> the UART is disabled if the prescaler is 0).
> 
> However, it seems that the prescaler was read back as 0 on a rockchip board
> which caused chars to be missing from the console output.
> 
> See this mail:
> https://lists.denx.de/pipermail/u-boot/2018-December/350355.html
> 
> I checked with Henri and did not find a solution so I reverted the patch:
> https://patchwork.ozlabs.org/patch/1007211/
> 
> Keeping this patch but only for selected platforms would be my favourite, but it
> would at least mean we need yet another debug UART selection, plus some changes
> to make the "prescaler == 0" detection specific to this new debug UART.
> Would this be better acceptable?

Doesn't the DT compatible tell you the UART type ? It does, so you can
match on that and apply the workaround accordingly . Or you can cache
the prescaler.

-- 
Best regards,
Marek Vasut