linux-kernel - Re: [PATCH v2 1/1] MIPS: Add Kconfig variable for CPUs with unaligned load/store instructions

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Date:   Thu, 27 Sep 2018 01:31:42 +0300
From:   Yasha Cherikovsky <yasha.che3@...il.com>
To:     Paul Burton <paul.burton@...s.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] MIPS: Add Kconfig variable for CPUs with
 unaligned load/store instructions

Hi Paul,

On Wed, 2018-09-26 at 22:18 +0000, Paul Burton wrote:
> Hi Yasha,
> 
> On Wed, Sep 26, 2018 at 02:16:15PM +0300, Yasha Cherikovsky wrote:
> > MIPSR6 CPUs do not support unaligned load/store instructions
> > (LWL, LWR, SWL, SWR and LDL, LDR, SDL, SDR for 64bit).
> > 
> > Currently the MIPS tree has some special cases to avoid these
> > instructions, and the code is testing for !CONFIG_CPU_MIPSR6.
> > 
> > This patch declares a new Kconfig variable:
> > CONFIG_CPU_HAS_LOAD_STORE_LR.
> > This variable indicates that the CPU supports these instructions.
> > 
> > Then, the patch does the following:
> > - Carefully selects this option on all CPUs except MIPSR6.
> > - Switches all the special cases to test for the new variable,
> >   and inverts the logic:
> >     '#ifndef CONFIG_CPU_MIPSR6' turns into
> >     '#ifdef CONFIG_CPU_HAS_LOAD_STORE_LR'
> >     and vice-versa.
> > 
> > Also, when this variable is NOT selected (e.g. MIPSR6),
> > CONFIG_GENERIC_CSUM will default to 'y', to compile generic
> > C checksum code (instead of special assembly code that uses the
> > unsupported instructions).
> > 
> > This commit should not affect any existing CPU, and is required
> > for future Lexra CPU support, that misses these instructions too.
> > 
> > Signed-off-by: Yasha Cherikovsky <yasha.che3@...il.com>
> > Cc: Ralf Baechle <ralf@...ux-mips.org>
> > Cc: Paul Burton <paul.burton@...s.com>
> > Cc: James Hogan <jhogan@...nel.org>
> > Cc: linux-mips@...ux-mips.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  arch/mips/Kconfig            | 35 +++++++++++++++++++++++++--
> >  arch/mips/kernel/unaligned.c | 47 ++++++++++++++++++------------------
> >  arch/mips/lib/memcpy.S       | 10 ++++----
> >  arch/mips/lib/memset.S       | 12 ++++-----
> >  4 files changed, 67 insertions(+), 37 deletions(-)
> 
> Thanks - applied to mips-next for 4.20.
> 
> Paul

Thanks!

Yasha