linux-kernel - Re: [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu

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Message-ID: <CAL_JsqKyRby5tp2JS1COodYf7F7sB_DJivyAe7FqQivp4KM6OA@mail.gmail.com>
Date:   Fri, 16 Oct 2020 08:19:47 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Jeremy Linton <jeremy.linton@....com>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 3/8] of/address: Introduce of_dma_get_max_cpu_address()

On Thu, Oct 15, 2020 at 12:42 AM Christoph Hellwig <hch@....de> wrote:
>
> > +phys_addr_t __init of_dma_get_max_cpu_address(struct device_node *np)
> > +{
> > +     phys_addr_t max_cpu_addr = PHYS_ADDR_MAX;
> > +     struct of_range_parser parser;
> > +     phys_addr_t subtree_max_addr;
> > +     struct device_node *child;
> > +     phys_addr_t cpu_end = 0;
> > +     struct of_range range;
> > +     const __be32 *ranges;
> > +     int len;
> > +
> > +     if (!np)
> > +             np = of_root;
>
> Requiring of_root to be passed explicitly would seem more natural
> to me than the magic NULL argument.  There doesn't seem to be any
> precedent for that kind of calling convention either.

I prefer that of_root is not more widely exposed and NULL regularly
means 'the whole tree'.

Rob