linux-kernel - Re: [RFT PATCH v3 21/27] tty: serial: samsung

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Date:   Sun, 7 Mar 2021 17:01:55 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Hector Martin <marcan@...can.st>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Will Deacon <will@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Documentation List <linux-doc@...r.kernel.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH v3 21/27] tty: serial: samsung_tty: IRQ rework

On Sun, Mar 7, 2021 at 12:34 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...onical.com> wrote:
> On 05/03/2021 17:29, Hector Martin wrote:
> > On 06/03/2021 01.20, Andy Shevchenko wrote:
> >>> I am just splitting an
> >>> existing function into two, where one takes the lock and the other does
> >>> the work. Do you mean using a different locking function? I'm not
> >>> entirely sure what you're suggesting.
> >>
> >> Yes, as a prerequisite
> >>
> >> spin_lock_irqsave -> spin_lock().
> >
> > Krzysztof, is this something you want in this series? I was trying to
> > avoid logic changes to the non-Apple paths.
>
> I don't quite get the need for such change (the code will be still
> called in interrupt handler, right?), but assuming the "why?" is
> properly documented, it can be a separate patch here.

This is only for readability: the common rule is to not disable
interrupts when they are already disabled, so a reader might wonder
if this instance of the handler is special in some case that it might
be called with interrupts enabled.

There is also a small overhead in accessing the global irq mask
register on some architectures, but for a uart that does not make
any difference of course.

While I'm generally in favor of that kind of cleanup, I'd also
prefer to leave it out of this series -- once you get into details
like this the series gets harder to review.

        Arnd