linux-kernel - Re: [PATCH v4 2/8] MIPS: Octeon: Enable LMTDMA/LMTST operations.

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Date:   Thu, 30 Nov 2017 23:12:01 +0000
From:   James Hogan <james.hogan@...s.com>
To:     David Daney <ddaney@...iumnetworks.com>
CC:     David Daney <david.daney@...ium.com>, <linux-mips@...ux-mips.org>,
        <ralf@...ux-mips.org>, <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <devel@...verdev.osuosl.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>,
        "Steven J. Hill" <steven.hill@...ium.com>,
        <devicetree@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Carlos Munoz <cmunoz@...ium.com>
Subject: Re: [PATCH v4 2/8] MIPS: Octeon: Enable LMTDMA/LMTST operations.

On Thu, Nov 30, 2017 at 03:09:33PM -0800, David Daney wrote:
> On 11/30/2017 02:56 PM, James Hogan wrote:
> > On Thu, Nov 30, 2017 at 01:49:43PM -0800, David Daney wrote:
> >> On 11/30/2017 01:36 PM, James Hogan wrote:
> >>> On Tue, Nov 28, 2017 at 04:55:34PM -0800, David Daney wrote:
> >>>> Signed-off-by: Carlos Munoz <cmunoz@...ium.com>
> >>>> Signed-off-by: Steven J. Hill <Steven.Hill@...ium.com>
> >>>> Signed-off-by: David Daney <david.daney@...ium.com>
> >>>> ---
> >>>>    arch/mips/cavium-octeon/setup.c       |  6 ++++++
> >>>>    arch/mips/include/asm/octeon/octeon.h | 12 ++++++++++--
> >>>>    2 files changed, 16 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
> >>>> index a8034d0dcade..99e6a68bc652 100644
> >>>> --- a/arch/mips/cavium-octeon/setup.c
> >>>> +++ b/arch/mips/cavium-octeon/setup.c
> >>>> @@ -609,6 +609,12 @@ void octeon_user_io_init(void)
> >>>>    #else
> >>>>    	cvmmemctl.s.cvmsegenak = 0;
> >>>>    #endif
> >>>> +	if (OCTEON_IS_OCTEON3()) {
> >>>> +		/* Enable LMTDMA */
> >>>> +		cvmmemctl.s.lmtena = 1;
> >>>> +		/* Scratch line to use for LMT operation */
> >>>> +		cvmmemctl.s.lmtline = 2;
> >>>
> >>> Out of curiosity, is there significance to the value 2 and associated
> >>> virtual address 0xffffffffffff8100, or is it pretty arbitrary?
> >>
> >> Yes, there is significance.
> >>
> >> CPU local memory starts at 0xffffffffffff8000, each line is 0x80 bytes.
> >> so the 2nd line starts at 0xffffffffffff8100
> > 
> > What I mean is, why is 2 chosen instead of any other value?
> 
> That is explained in the change log of patch 5/8:
> 
> 
>      1st 128-bytes: Use by IOBDMA
>      2nd 128-bytes: Reserved by kernel for scratch/TLS emulation.
>      3rd 128-bytes: OCTEON-III LMTLINE

Ah yes. Perhaps it deserves a brief comment in the code, or even an
enum.

Cheers
James

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