linux-kernel - Re: [PATCH] csky: Fix a size determination in gpr

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Message-ID: <20200923045231.GH3421308@ZenIV.linux.org.uk>
Date:   Wed, 23 Sep 2020 05:52:31 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Guo Ren <guoren@...nel.org>
Cc:     Zhenzhong Duan <zhenzhong.duan@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] csky: Fix a size determination in gpr_get()

On Wed, Sep 23, 2020 at 10:37:31AM +0800, Guo Ren wrote:

> > What's going on there?  The mapping is really weird - assuming
> > you had v0..v31 in the first 32 elements of regs->vr[], you
> > end up with
> >
> > v0 v1 v2 v3 v2 v3 v6 v7 v4 v5 v10 v11 v6 v7 v14 v15
> > v8 v9 v18 v19 v10 v11 v22 v23 v12 v13 v26 v27 v14 v15 v30 v31
> >
> > in the beginning of the output.  Assuming it is the intended
> > behaviour, it's probably worth some comments...
> FPU & VDSP use the same regs. 32 FPU regs' width is 64b and 16 VDSP
> regs' width is 128b.
> 
> vr[0], vr[1] = fp[0] & vr[0] vr[1], vr[2], vr[3] = vdsp reg[0]
> ...
> vr[60], vr[61] = fp[15] & vr[60] vr[61], vr[62], vr[63] = vdsp reg[15]
> vr[64], vr[65] = fp[16]
> vr[66], vr[67] = fp[17]
> ...
> vr[94], vr[95] = fp[31]
> 
> Yeah, this is confusing and I'll add a comment later.

Umm...  It would help if you described these 3 layouts:
	1) kernel-side with VDSP
	2) userland (identical to (1)?)
	3) kernel-side without VDSP
Still confused...

PS: my apologies re commit message - I left a note to myself when doing
that series and then forgot about it ;-/

Anyway, which tree should it go through?  In any case, that fix is
Acked-by: Al Viro <viro@...iv.linux.org.uk>
and I can take it through vfs.git or you guys can pick in csky tree;
up to you.