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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Fri, 26 Feb 2021 19:06:43 +0100
Message-ID: <CAK8P3a03BcXZu+On885GaR547SHJYtiu3d_QHG0zOr2UiKn6qQ@mail.gmail.com>
Subject: Re: [RFC 13/13] scsi: megaraid: Make use of dev_64bit_mmio_supported()
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        DTML <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Arnd Bergmann <arnd@arndb.de>, Will Deacon <will@kernel.org>
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On Fri, Feb 26, 2021 at 3:30 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Fri, Feb 26, 2021 at 3:03 PM Nicolas Saenz Julienne
> <nsaenzjulienne@suse.de> wrote:
>
> >         unsigned long flags;
> > -       spin_lock_irqsave(&instance->hba_lock, flags);
> > -       writel(le32_to_cpu(req_desc->u.low),
> > -               &instance->reg_set->inbound_low_queue_port);
> > -       writel(le32_to_cpu(req_desc->u.high),
> > -               &instance->reg_set->inbound_high_queue_port);
> > -       spin_unlock_irqrestore(&instance->hba_lock, flags);
>
> > +
> > +       if (dev_64bit_mmio_supported(&instance->pdev->dev)) {
> > +               writeq(req_data, &instance->reg_set->inbound_low_queue_port);
> > +       } else {
> > +               spin_lock_irqsave(&instance->hba_lock, flags);
> > +               lo_hi_writeq(req_data, &instance->reg_set->inbound_low_queue_port);
> > +               spin_unlock_irqrestore(&instance->hba_lock, flags);
> > +       }
>
> I see your patch changes the code to the lo_hi_writeq() accessor,
> and it also fixes the endianness bug (double byteswap on big-endian),
> but it does not fix the spinlock bug (writel on pci leaks out of the lock
> unless it's followed by a read).

On second look, it seems your patch breaks the byteorder logic,
rather than fixing it. It would seem better to leave it unchanged
then, or to send a separate rework of the endianness conversion if
you think it is wrong.

       Arnd