linux-kernel - Re: [PATCH v5 3/6] iomap: introduce io{read|write}64_{lo_hi|hi

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Date:   Mon, 31 Jul 2017 09:55:45 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-ntb@...glegroups.com,
        linux-crypto <linux-crypto@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Horia Geantă <horia.geanta@....com>,
        Stephen Bates <sbates@...thlin.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Suresh Warrier <warrier@...ux.vnet.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH v5 3/6] iomap: introduce io{read|write}64_{lo_hi|hi_lo}



On 30/07/17 10:03 AM, Andy Shevchenko wrote:
> On Thu, Jul 27, 2017 at 2:19 AM, Logan Gunthorpe <logang@...tatee.com> wrote:
>> In order to provide non-atomic functions for io{read|write}64 that will
>> use readq and writeq when appropriate. We define a number of variants
>> of these functions in the generic iomap that will do non-atomic
>> operations on pio but atomic operations on mmio.
>>
>> These functions are only defined if readq and writeq are defined. If
>> they are not, then the wrappers that always use non-atomic operations
>> from include/linux/io-64-nonatomic*.h will be used.
> 
> Don't you see here a slight problem?
> 
> In some cases we want to substitute atomic in favour of non-atomic
> when both are defined.
> So, please don't do this "smartly".

I'm not sure what you mean here. The driver should use ioread64 and
include an io-64-nonatomic header. Then there are three cases:

1) The arch has no atomic 64 bit io operations defined. In this case it
uses the non-atomic inline function in the io-64-nonatomic header.

2) The arch uses CONFIG_GENERIC_IOMAP and has readq defined, but not
ioread64 defined (likely because pio can't do atomic 64 bit operations
but mmio can). In this case we need to use the ioread64_xx functions
defined in iomap.c which do atomic mmio and non-atomic pio.

3) The arch has ioread64 defined so the atomic operation is used.

>> +u64 ioread64_lo_hi(void __iomem *addr)
>> +{
>> +       IO_COND(addr, return pio_read64_lo_hi(port), return readq(addr));
>> +       return 0xffffffffffffffffLL;
>> +}
> 
> U missed u.

I'll fix this in the next revision.

Thanks,

Logan