linux-kernel - Re: [PATCH v1 2/2] mtd: rawnand: Add NAND controller support on Intel LGM SoC

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Date:   Thu, 16 Apr 2020 15:51:32 +0200
From:   John Crispin <john@...ozen.org>
To:     Arnd Bergmann <arnd@...db.de>,
        Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "Ramuthevar, Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Anders Roxell <anders.roxell@...aro.org>,
        Andriy Shevchenko <andriy.shevchenko@...el.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        cheol.yong.kim@...el.com, devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:MEMORY TECHNOLOGY..." <linux-mtd@...ts.infradead.org>,
        masonccyang@...c.com.tw, Miquel Raynal <miquel.raynal@...tlin.com>,
        Piotr Sroka <piotrs@...ence.com>, qi-ming.wu@...el.com,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>, Vignesh R <vigneshr@...com>,
        Songjun Wu <songjun.wu@...ux.intel.com>,
        hua.ma@...ux.intel.com, yixin.zhu@...ux.intel.com,
        chuanhua.lei@...ux.intel.com, Hauke Mehrtens <hauke@...ke-m.de>
Subject: Re: [PATCH v1 2/2] mtd: rawnand: Add NAND controller support on Intel
 LGM SoC

On 16.04.20 15:20, Arnd Bergmann wrote:
> On Thu, Apr 16, 2020 at 2:40 PM Boris Brezillon
> <boris.brezillon@...labora.com> wrote:
>> On Thu, 16 Apr 2020 15:26:51 +0300
>> Andy Shevchenko <andy.shevchenko@...il.com> wrote:
>>> On Thu, Apr 16, 2020 at 3:03 PM Boris Brezillon
>>> <boris.brezillon@...labora.com> wrote:
>>>> On Thu, 16 Apr 2020 19:38:03 +0800
>>>> Note that the NAND subsystem is full of unmaintained legacy drivers, so
>>>> every time we see someone who could help us get rid or update one of
>>>> them we have to take this opportunity.
>>>
>>> Don't we rather insist to have a MAINTAINERS record for new code to
>>> avoid (or delay at least) the fate of the legacy drivers?
>>>
>>
>> Well, that's what we do for new drivers, but the xway driver has been
>> added in 2012 and the policy was not enforced at that time. BTW, that
>> goes for most of the legacy drivers in have in the NAND subsystems
>> (some of them even predate the git era).
>>
>> To be clear, I just checked and there's no official maintainer for this
>> driver. Best option would be to Cc the original author and contributors
>> who proposed functional changes to the code, as well as the MIPS
>> maintainers (Xway is a MIPS platform).
> 
> A lot of the pre-acquisition code for lantiq was contributed by Hauke
> Mehrtens and John Crispin. There was an intermediate generation of
> MIPS SoCs with patches posted for review  by Intel in 2018 (presumably
> by the same organizatiob), but those were never resubmitted after v2
> and never merged:
> 
> https://lore.kernel.org/linux-mips/20180803030237.3366-1-songjun.wu@linux.intel.com/
> 
>          Arnd
> 

Hi,

the legacy Mips SoC had a External Bus Unit (EBU), similar to an 
Intel/Hitachi style bus. It was used back then for lots of things, 
sometimes driving Leds via 74* latches, Arcadyan used it for external 
reset lines and very rarely was it used for nand.

Looking at this series and comparing it with xway_nand.c we see that the 
init sequence is near identical. Best guess is that the mountain lion 
uses an internal block very similar to what the legacy mips silicon used 
just in a newer generation and the new proposed driver is more feature 
complete.

If this is the case ideally the xway_nand.c is dropped and that silicon 
is made working with the newer driver. Chances are that we just need to 
add a "support less features" style flag.

Unfortunately i no longer have the evalkit for the Mips SoCs.

    John