linux-kernel - Re: [RFC PATCH 06/13] switchtec_ntb: initialize hardware for memory windows

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Date:   Sat, 17 Jun 2017 10:39:35 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-ntb@...glegroups.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <Allen.Hubbe@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 06/13] switchtec_ntb: initialize hardware for memory
 windows

On 16/06/17 11:16 PM, Greg Kroah-Hartman wrote:
>> +#ifndef ioread64
>> +#ifdef readq
>> +#define ioread64 readq
>> +#else
>> +#define ioread64 _ioread64
>> +static inline u64 _ioread64(void __iomem *mmio)
>> +{
>> +	u64 low, high;
>> +
>> +	low = ioread32(mmio);
>> +	high = ioread32(mmio + sizeof(u32));
>> +	return low | (high << 32);
>> +}
>> +#endif
>> +#endif
> 
> Really?  Don't we have ioread64 in generic code for all arches?  If not,
> that should be fixed, don't hide this in a random driver please.  Or
> just restrict your driver to only building on those arches that does
> provide this api.

Yes, I know these are _very_ ugly. Unfortunately, the other ntb drivers
each have the exact same thing. ioread64 is not provided universally at
this time and I did spend a bit of time digging and things are a bit
messy so I wasn't at all sure of the correct solution.

For starters, ioread64 is only defined on 64 bit machines. They are
surrounded by ifdef CONFIG_64BIT and it's not clear to me if the above
wrapper (around two ioread32s) would be acceptable universally.

Second, the x86_64 version doesn't even compile. This is because the
arch doesn't provide any ioread64 implementation anywhere and the macro
in io.h isn't used because CONFIG_GENERIC_IOMAP is defined.

The only arch where I _think_ ioread64 would work is powerpc or any that
define CONFIG_64BIT and not CONFIG_GENERIC_IOMAP.

If you have any guidance on this I'd be happy to try and make a patch or
two for it.

Thanks,

Logan