linux-kernel - Re: [PATCH 0/3] Add __ioread32

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Message-ID: <20150916005053.GL23081@codeaurora.org>
Date:	Tue, 15 Sep 2015 17:50:53 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andy Gross <agross@...eaurora.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-soc@...r.kernel.org,
	linux-mips@...ux-mips.org, Hauke Mehrtens <hauke@...ke-m.de>,
	Paul Walmsley <paul@...an.com>,
	Rafał Miłecki <zajec5@...il.com>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 0/3] Add __ioread32_copy() and use it

On 09/15, Andrew Morton wrote:
> On Tue, 15 Sep 2015 12:41:26 -0700 Stephen Boyd <sboyd@...eaurora.org> wrote:
> 
> > The SMD driver is reading and writing chunks of data to iomem,
> > and there's an __iowrite32_copy() function for the writing part, but
> > no __ioread32_copy() function for the reading part. This series
> > adds __ioread32_copy() and uses it in two places. Andrew is on Cc in
> > case this should go through the -mm tree. Otherwise the target
> > of this patch series is SMD, so I've sent it to Andy.
> 
> "soc: qcom: smd: Use __ioread32_copy() instead of open-coding it" no
> longer applies, because smd_copy_from_fifo() has switched to
> readl_relaxed().

Yes. There are some other patches in flight on the mailing list
to this file from me[1]. Those would need to be applied first to
avoid conflicts.

> 
> Let's use the __weak macro rather than open-coding it (and convert
> __iowrite32_copy() while we're in there).

Yep, I converted the __iowrite32_copy() open-code in there too in
the patch series I mentioned above. See [2].

> 
> It's unclear why __iowrite32_copy() is a weak function - nothing
> overrides it.  Perhaps we should just take that away rather than
> copying it into __ioread32_copy().

Huh? I see that x86 has an implementation in arch/x86/lib/iomap_copy_64.S

> 
> __iowrite32_copy() is marked __visible.  I don't actually know what
> that does and Andi's d47d5c8194579bc changelog (which sucks the big
> one) didn't explain it.  Apparently it has something to do with being
> implemented in assembly, but zillions of functions are implemented in
> assembly, so why are only two functions marked this way?  Anyway,
> __ioread32_copy() is implemented in C so I guess __visible isn't needed
> there.

Yeah, I didn't add visible because there isn't an assembly
version of __ioread32_copy() so far. I can remove __weak if
desired. I left it there to match __iowrite32_copy() in case
x86 wanted to override it but we can do that later or never.

[1] http://lkml.kernel.org/g/1441234011-4259-7-git-send-email-sboyd@codeaurora.org
[2] http://lkml.kernel.org/g/1441234011-4259-5-git-send-email-sboyd@codeaurora.org

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