linux-kernel - Re: [PATCH AUTOSEL 6.14 636/642] serial: sh-sci: Save and restore more registers

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Message-ID: <CAMuHMdXzu1oP5hKAFFjqZ0T=d8jG8eqsTmeX5RKdjLB-jFCPMw@mail.gmail.com>
Date: Tue, 6 May 2025 08:47:09 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, jirislaby@...nel.org, 
	wsa+renesas@...g-engineering.com, zack.rusin@...adcom.com, 
	namcao@...utronix.de, prabhakar.mahadev-lad.rj@...renesas.com, 
	linux-serial@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.14 636/642] serial: sh-sci: Save and restore
 more registers

Hi Sasha,

On Tue, 6 May 2025 at 00:39, Sasha Levin <sashal@...nel.org> wrote:
> From: Geert Uytterhoeven <geert+renesas@...der.be>
>
> [ Upstream commit 81100b9a7b0515132996d62a7a676a77676cb6e3 ]
>
> 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 BRG Frequency
> Division (SCDL) and Clock Select (SCCKS) registers as well.
>
> Also save and restore the HSCIF's Sampling Rate Register (HSSRR), which
> configures the sampling point, and the SCIFA/SCIFB's Serial Port Control
> and Data Registers (SCPCR/SCPDR), which configure the optional control
> flow signals.
>
> After this, all registers that are not saved/restored are either:
>   - read-only,
>   - write-only,
>   - status registers containing flags with clear-after-set semantics,
>   - FIFO Data Count Trigger registers, which do not matter much for
>     the serial console.

Please make sure to backport this to v6.1, v6.6, and v6.12, too,
as the commit this fixes:

> Fixes: 22a6984c5b5df8ea ("serial: sh-sci: Update the suspend/resume support")

is already queued for v6.1, v6.6, and v6.12.

> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Tested-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> Reviewed-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> Link: https://lore.kernel.org/r/11c2eab45d48211e75d8b8202cce60400880fe55.1741114989.git.geert+renesas@glider.be
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

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