linux-kernel - Re: [PATCH] serial: sh-sci: Save and restore SCDL and SCCKS

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Message-ID: <CAMuHMdWb1=Jqu3ADtNvPUZOzLZqPjxaBS6wZm6XJ=aYR8PU=pw@mail.gmail.com>
Date: Wed, 19 Feb 2025 16:55:37 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Claudiu Beznea <claudiu.beznea@...on.dev>
Cc: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, linux-serial@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: sh-sci: Save and restore SCDL and SCCKS

Hi Claudiu,

On Wed, 19 Feb 2025 at 16:04, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> On 19.02.2025 16:24, Geert Uytterhoeven wrote:
> > On (H)SCIF with a Baud Rate Generator for External Clock (BRG), there
> > are multiple ways to configure the requested serial speed.  If firmware
> > uses a different method than Linux, and if any debug info is printed
> > after the Bit Rate Register (SCBRR) is restored, but before termios is
> > reconfigured (which configures the alternative method), the system may
> > lock-up during resume.
> >
> > Fix this by saving and restoring the contents of the Frequency Division
> > (DL) and Clock Select (CKS) registers as well.
>
> Keeping the thinks RZ/G3S focused (as proposed in the first versions of
> this support), I missed there might be other registers on other IP variants.

Indeed. I forgot to mention I didn't check other registers...

> Reviewing the full list of registers from [1], maybe the HSSRR and
> SCPCR should be saved/restored as well?

Agreed. Late restoring these is probably never fatal, though.

> [1]
> https://elixir.bootlin.com/linux/v6.13.3/source/drivers/tty/serial/sh-sci.h#L14
>
> >
> > Fixes: 22a6984c5b5df8ea ("serial: sh-sci: Update the suspend/resume support")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> For this patch:
> Tested-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds