Re: [PATCH v2 08/11] serial: 8250_dw: Add Sophgo SG2042 support

Chen Wang
2023-09-22T11:39:13Z

Regards,

unicornx

Emil Renner Berthing <emil.renner.berthing@canonical.com> 于2023年9月22日周五 18:40写道：
>
> Ben Dooks wrote:
> > On 20/09/2023 07:40, Chen Wang wrote:
> > > From: Emil Renner Berthing <emil.renner.berthing@canonical.com>
> > >
> > > Add quirk to skip setting the input clock rate for the uarts on the
> > > Sophgo SG2042 SoC similar to the StarFive JH7100.
> >
> > I'd love an actual explanation of why this is necessary here.
>
> Makes sense. For the JH7100 the commit message is:
>
> On the StarFive JH7100 RISC-V SoC the UART core clocks can't be set to
> exactly 16 * 115200Hz and many other common bitrates. Trying this will
> only result in a higher input clock, but low enough that the UART's
> internal divisor can't come close enough to the baud rate target.
> So rather than try to set the input clock it's better to skip the
> clk_set_rate call and rely solely on the UART's internal divisor.
>
> @Chen Wang is this also true for the SG2042?
>
> /Emil

Emil & Ben,
I need to double-confirm this with sophgo engineers. Because they are
off work now, I will probably get back to you later next week.