linux-kernel - Re: [RESEND2 PATCH 1/3] memremap: add MEMREMAP

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Message-ID: <20160217115347.GA28433@e106950-lin.cambridge.arm.com>
Date:	Wed, 17 Feb 2016 11:53:48 +0000
From:	Brian Starkey <brian.starkey@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND2 PATCH 1/3] memremap: add MEMREMAP_WC flag

Hi Andrew,

Would you pick these up if I rebase onto linux-next?

How strongly do you feel about the input argument modification vs.
staying in-line with the rest of the function?

Thanks,

Brian

On Tue, Feb 09, 2016 at 10:23:00AM +0000, Brian Starkey wrote:
>Hi Andrew,
>
>Thanks for taking a look,
>
>On Mon, Feb 08, 2016 at 12:03:17PM -0800, Andrew Morton wrote:
>>On Mon,  8 Feb 2016 17:30:50 +0000 Brian Starkey <brian.starkey@....com> wrote:
>>The patch generally looks OK to me.  It generates rejects against
>>linux-next because of some janitorial changes in memremap.c.
>>
>
>Ah yeah, so it does - sorry. I was hoping this could make it into 4.5,
>but I can rebase onto linux-next if that's better. Annoyingly it only
>conflicts because of a couple of quotation marks.
>
>>
>>>@@ -101,6 +107,11 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)
>>> 		addr = ioremap_wt(offset, size);
>>> 	}
>>>
>>>+	if (!addr && (flags & MEMREMAP_WC)) {
>>>+		flags &= ~MEMREMAP_WC;
>>>+		addr = ioremap_wc(offset, size);
>>>+	}
>>>+
>>> 	return addr;
>>> }
>>
>>The modifications of `flags' is unneeded (and the compiler will remove
>>it).  And generally the modification of incoming args is a bit nasty
>>IMO - I find it's better to treat them as const - part of the calling
>>environment which can be relied upon to be unaltered as the code
>>evolves.
>>
>
>To be honest I was just mirroring the rest of the function. I guess
>the idea was filtering the different mapping types in case one of the
>'mappers' can handle multiple flags or something. I'll remove it if
>you like, I just thought that extending the functionality in-keeping
>with the current semantics was a better evolution - let me know.
>
>Thanks,
>Brian