linux-kernel - Re: [PATCH 1/2] dma-mapping: introduce dma_get_seg_boundary_nr

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Message-ID: <20200903161252.GA24841@lst.de>
Date:   Thu, 3 Sep 2020 18:12:52 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Nicolin Chen <nicoleotsuka@...il.com>,
        Christoph Hellwig <hch@....de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        rth@...ddle.net, ink@...assic.park.msu.ru,
        Matt Turner <mattst88@...il.com>, linux-alpha@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org,
        schnelle@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        hca@...ux.ibm.com, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        sparclinux@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, linux-parisc@...r.kernel.org
Subject: Re: [PATCH 1/2] dma-mapping: introduce
 dma_get_seg_boundary_nr_pages()

On Thu, Sep 03, 2020 at 01:57:39PM +0300, Andy Shevchenko wrote:
> > +{
> > +       if (!dev)
> > +               return (U32_MAX >> page_shift) + 1;
> > +       return (dma_get_seg_boundary(dev) >> page_shift) + 1;
> 
> Can it be better to do something like
>   unsigned long boundary = dev ? dma_get_seg_boundary(dev) : U32_MAX;
> 
>   return (boundary >> page_shift) + 1;
> 
> ?

I don't really see what that would buy us.