linux-kernel - Re: [PATCH] ARM: vfp: fix fpsid register subarchitecture field mask width

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Message-ID: <20130222182705.GC19527@mudshark.cambridge.arm.com>
Date:	Fri, 22 Feb 2013 18:27:06 +0000
From:	Will Deacon <will.deacon@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	Steve Muckle <smuckle@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: vfp: fix fpsid register subarchitecture field mask
 width

Hi guys,

On Fri, Feb 22, 2013 at 08:08:05AM +0000, Stephen Boyd wrote:
> From: Steve Muckle <smuckle@...eaurora.org>
> 
> The subarchitecture field in the fpsid register is 7 bits wide.
> The topmost bit is used to designate that the subarchitecture
> designer is not ARM. We use this field to determine which VFP
> version is supported by the CPU. Since the topmost bit is masked
> off we detect non-ARM subarchitectures as supporting only
> HWCAP_VFP and not HWCAP_VFPv3 as it should be for Qualcomm's
> processors.

I'm struggling to see why this has anything to do with the hwcaps being set
incorrectly. What value do you have in fpsid? As far as I can tell, the
subarchitecture bits 6:0 should start at 0x40 for you, right?

I can see cases for changing this code, I just don't see why it would go
wrong in the case you're describing.

Cheers,

Will
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