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

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Message-ID: <CAKNVLfZ0ndwGUUq0VX3vdvxfDK6Shf61WS_dC5WocChKeYSWJg@mail.gmail.com>
Date:   Wed, 19 Oct 2022 18:19:13 +0300
From:   Siarhei Volkau <lis8215@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Arnd Bergmann <arnd@...db.de>, kernel test robot <lkp@...el.com>,
        kbuild-all@...ts.01.org,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dmaengine@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-mips@...r.kernel.org,
        GPIO SUBSYSTEM <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 7/8] serial: 8250/ingenic: Add support for the
 JZ4750/JZ4755 SoCs

пн, 17 окт. 2022 г. в 12:32, Paul Cercueil <paul@...pouillou.net>:
> > 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.

Agree, the vendor's kernel does that as well.

Also I found that:
1. Many other drivers compile the early console only when
CONFIG_SERIAL_8250_CONSOLE is set.
2. All the early ingenic_ functions can be labeled as __init.
Shall I fix that while I'm already here?