Re: [PATCH 7/8] serial: 8250/ingenic: Add support for the JZ4750/JZ4755 SoCs

[Paul Cercueil <paul@crapouillou.net>]

Hi Siarhei,

Le dim., oct. 16 2022 at 21:39:48 +0300, Siarhei Volkau 
<lis8215@gmail.com> a écrit :
> чт, 13 окт. 2022 г. в 21:56, Siarhei Volkau 
> <lis8215@gmail.com>:
> 
>>  > Just disable the divider in ingenic_fixup_fdt() in
> 
>>  I'll check that.
> 
> I checked that approach: serial seems to be working as expected,
> but not all the time: there's a time period when the CGU driver
> started but serial console driver is still early one.
> In my case UART produces garbage at that period since CGU
> needs to enable clock divider back: ext is 24MHz but 12MHz
> required for audio codec and USB to function properly.

What I'd do, is just force-enable it to 12 MHz in ingenic_fixup_fdt(), 
since the programming manual basically says that 24 MHz does not work 
properly.

Then in the earlycon setup code hardcode the /2 divider with a big fat 
comment about why it's there.

Cheers,
-Paul

> So I think Arnd's approach:
> 
>>  the hardware should already be in a working state,
>>  with no need to touch it during early boot.
> 
> shall resolve the problem, although I can't check it on all supported
> hardware.
> 
> BR,
> Siarhei