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

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Date:   Thu, 3 Sep 2020 19:53:07 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Christoph Hellwig <hch@....de>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     linux-ia64@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>, sparclinux@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Helge Deller <deller@....de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Matt Turner <mattst88@...il.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, schnelle@...ux.ibm.com,
        hca@...ux.ibm.com, Nicolin Chen <nicoleotsuka@...il.com>,
        ink@...assic.park.msu.ru, Thomas Gleixner <tglx@...utronix.de>,
        gerald.schaefer@...ux.ibm.com, rth@...ddle.net,
        Tony Luck <tony.luck@...el.com>, linux-parisc@...r.kernel.org,
        linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-alpha@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/2] dma-mapping: introduce
 dma_get_seg_boundary_nr_pages()



Le 03/09/2020 à 18:12, Christoph Hellwig a écrit :
> 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.
> 

I guess it would avoid the duplication of    >> page_shift) + 1

Christophe