linux-kernel - Re: [PATCH 05/13] tty: serial: samsung: add gs101 earlycon support

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Date:   Thu, 14 Dec 2023 14:19:44 +0000
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Tudor Ambarus" <tudor.ambarus@...aro.org>,
        "Peter Griffin" <peter.griffin@...aro.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        krzysztof.kozlowski+dt@...aro.org,
        "Michael Turquette" <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Conor Dooley" <conor+dt@...nel.org>, andi.shyti@...nel.org,
        "Alim Akhtar" <alim.akhtar@...sung.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Jiri Slaby" <jirislaby@...nel.org>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>,
        "Sylwester Nawrocki" <s.nawrocki@...sung.com>,
        "Tomasz Figa" <tomasz.figa@...il.com>,
        "Chanwoo Choi" <cw00.choi@...sung.com>,
        "Sam Protsenko" <semen.protsenko@...aro.org>
Cc:     André Draszik <andre.draszik@...aro.org>,
        saravanak@...gle.com, "William McVicker" <willmcvicker@...gle.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 05/13] tty: serial: samsung: add gs101 earlycon support

On Thu, Dec 14, 2023, at 13:52, Tudor Ambarus wrote:
> On 12/14/23 12:01, Arnd Bergmann wrote:
>> On Thu, Dec 14, 2023, at 11:52, Tudor Ambarus wrote:
>>> +static int __init gs101_early_console_setup(struct earlycon_device *device,
>> 
>
> It works if in device tree one specifies the reg-io-width property and
> sets it to 4. If the reg-io-width is not specified, the iotype defaults
> to UPIO_MEM causing the SError interrupt on gs101 which makes the system
> unusable.

In the case of incorrect DT data like a missing reg-io-width property,
I would expect it to still fail once the regular console or tty takes
over from earlycon.

> Also, if the earlycon comes specified from the kernel params, the
> of_setup_earlycon() is no longer called and the earlycon will be set
> solely based on the kernel params buffer, thus allowing users to crash
> the kernel on wrong earlycon definitions.

But that in turn is the same as specifying any other incorrect earlycon.

> If you think the change is fine, I can amend the commit message with the
> description from above.

I'm still not convinced we need a special case here when everything else
just requires passing the correct data.

     Arnd