linux-kernel - Re: [PATCH] serdev: Don't claim unsupported serial devices

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Message-ID: <875zicofof.fsf@kokedama.swc.toshiba.co.jp>
Date:   Thu, 19 Dec 2019 17:58:08 +0900
From:   Punit Agrawal <punit1.agrawal@...hiba.co.jp>
To:     Johan Hovold <johan@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        <linux-serial@...r.kernel.org>,
        "ACPI Devel Maling List" <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <nobuhiro1.iwamatsu@...hiba.co.jp>, <shrirang.bagul@...onical.com>,
        Stable <stable@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Hans de Goede" <hdegoede@...hat.com>
Subject: Re: [PATCH] serdev: Don't claim unsupported serial devices

Johan Hovold <johan@...nel.org> writes:

> On Thu, Dec 19, 2019 at 09:39:57AM +0100, Rafael J. Wysocki wrote:
>> On Wed, Dec 18, 2019 at 9:56 AM Johan Hovold <johan@...nel.org> wrote:
>> >
>> > On Wed, Dec 18, 2019 at 03:56:46PM +0900, Punit Agrawal wrote:
>> > > Serdev sub-system claims all serial devices that are not already
>> > > enumerated. As a result, no device node is created for serial port on
>> > > certain boards such as the Apollo Lake based UP2. This has the
>> > > unintended consequence of not being able to raise the login prompt via
>> > > serial connection.
>> > >
>> > > Introduce a blacklist to reject devices that should not be treated as
>> > > a serdev device. Add the Intel HS UART peripheral ids to the blacklist
>> > > to bring back serial port on SoCs carrying them.
>> > >
>> > > Cc: stable@...r.kernel.org
>> > > Signed-off-by: Punit Agrawal <punit1.agrawal@...hiba.co.jp>
>> > > Cc: Rob Herring <robh@...nel.org>
>> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> > > Cc: Johan Hovold <johan@...nel.org>
>> > > Cc: Hans de Goede <hdegoede@...hat.com>
>> > > ---
>> > >
>> > > Hi,
>> > >
>> > > The patch has been updated based on feedback recieved on the RFC[0].
>> > >
>> > > Please consider merging if there are no objections.
>> >
>> > Rafael, I vaguely remember you arguing for a white list when we
>> > discussed this at some conference. Do you have any objections to the
>> > blacklist approach taken here?
>> 
>> As a rule, I prefer whitelisting, because it only enables the feature
>> for systems where it has been tested and confirmed to work.
>> 
>> However, if you are convinced that in this particular case the feature
>> should work on the vast majority of systems with a few possible
>> exceptions, blacklisting is fine too.
>> 
>> It all depends on what the majority is, at least in principle.
>
> Ok, thanks. I don't have a preference either way in this case simply
> because I don't know the distribution you refer to.
>
> But if Hans thinks blacklisting is the way to go then let's do that. We
> haven't had that many reports about this, but if that were to change
> down the line, I guess we can always switch to whitelisting.
>
> Punit, feel free to add my
>
> Acked-by: Johan Hovold <johan@...nel.org>
>
> after addressing the review comments you've gotten so far.

Thanks Johan.

I will post a new version with the updates and acks.