linux-kernel - Re: [PATCH 1/1] clk: socfpga: gate: Fix of by factor 2 for serial console

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Message-ID: <20231006184020.7fb6f509@mitra>
Date:   Fri, 6 Oct 2023 18:40:36 +0200
From:   Benedikt Spranger <b.spranger@...utronix.de>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Dinh Nguyen <dinguyen@...nel.org>
Subject: Re: [PATCH 1/1] clk: socfpga: gate: Fix of by factor 2 for serial
 console

On Fri, 6 Oct 2023 17:01:34 +0200
Maxime Ripard <mripard@...nel.org> wrote:

> On Thu, Oct 05, 2023 at 08:32:23PM +0200, Benedikt Spranger wrote:
> > On Thu, 5 Oct 2023 13:34:01 +0200
> > Maxime Ripard <mripard@...nel.org> wrote:
> > 
> > > Where is that factor 2 coming from?
> > In drivers/tty/serial/8250/8250_dw.c p->uartclk is set twice as high,
> > as it should be: 
> > 
> > dw8250_set_termios() is called and rate is evaluated to 20000000 in the
> > bad and 10000000 in the good case. As a result p->uartclk is set to
> > 20000000 in the bad case.
> 
> Sure, sorry I worded that poorly. What I meant was what clock tree
> decision is taken now that wasn't taken before that leads to that factor
> 2 difference.
OK.

> Thanks for the traces, that's helpful. It looks like the culprit is:
> 
> Good:
> 
>             init-1       [001] .....     0.125643: clk_rate_request_start: l4_sp_clk min 0 max 4294967295, parent per_base_clk (200000000)
>             init-1       [001] .....     0.125651: clk_rate_request_done: l4_sp_clk min 0 max 4294967295, parent per_base_clk (200000000)
>             init-1       [001] .....     0.125657: dw8250_set_termios: dw8250_set_termios: rate = 200000000 newrate = 1843200
> 
> vs Bad:
> 
>             init-1       [001] .....     0.116063: clk_rate_request_start: l4_sp_clk min 0 max 4294967295, parent per_base_clk (200000000)
>             init-1       [001] .....     0.116089: clk_rate_request_done: l4_sp_clk min 0 max 4294967295, parent per_base_clk (200000000)
>             init-1       [001] .....     0.116096: dw8250_set_termios: dw8250_set_termios: rate = 4294967274 newrate = 1843200
> 
> The rate returned is super suspicious, as it's an -EINVAL casted into an
> unsigned long. So I think something on that clock chain is returning an
> error for some reason, which is then treated as a rate by the rest and
> everybody's just confused.
OK.

> What is the board that you're using?
I am using a Cyclone5 DE0-Nano-Soc/Atlas board
(socfpga_cyclone5_de0_nano_soc.dts). 

Regards
    Benedikt Spranger