linux-kernel - Re: [PATCH -next] dma-debug: Use %pa to format phys_addr

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Date:   Thu, 30 Mar 2023 09:07:33 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Desnes Nunes <desnesn@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>,
        noreply@...erman.id.au, Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH -next] dma-debug: Use %pa to format phys_addr_t

Hi Christoph,

On Thu, Mar 30, 2023 at 1:50 AM Christoph Hellwig <hch@...radead.org> wrote:
> I've applied this as it is the first fix I got into my mailbox for it.

Thank you!

> Arnd sent one a little later, which uses %pap instead of %pa, which
> confused me a bit.  The documentation seems to allow both without
> any recommendation which one to use, which confuses me even further.

The "%pa" class supports two variants: "%pad" (for dma_addr_t) and
"%pap" (for phys_addr_t). "%pa" is a shortcut for the latter, cfr.
https://elixir.bootlin.com/linux/latest/source/lib/vsprintf.c#L1792

The default exists because "%pa" was fist, cfr. commit aaf07621b8bbfdc0
("vsprintf: add %pad extension for dma_addr_t use"), and I don't think
we can easily remove it. The default is shorter (saves one byte, even
compared to %llx"), so why not use it?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds