linux-kernel - Re: [PATCH v2 1/2] mtd: nand: Add Cadence NAND controller driver

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Message-ID: <20190701102135.GA20033@global.cadence.com>
Date:   Mon, 1 Jul 2019 11:21:36 +0100
From:   Piotr Sroka <piotrs@...ence.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     <linux-kernel@...r.kernel.org>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Paul Burton <paul.burton@...s.com>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Marcel Ziswiler" <marcel.ziswiler@...adex.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Stefan Agner <stefan@...er.ch>, <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] mtd: nand: Add Cadence NAND controller driver

The 07/01/2019 12:04, Miquel Raynal wrote:
>EXTERNAL MAIL
>
>
>Hi Piotr,
>
>Piotr Sroka <piotrs@...ence.com> wrote on Mon, 1 Jul 2019 10:51:45
>+0100:
>
>
>[...]
>> >> >> >
>> >> >> >This driver is way too massive, I am pretty sure it can shrink a
>> >> >> >little bit more.
>> >> >> >[...]
>> >> >> >
>> >> >> I will try to make it shorer but it will be difucult to achive. It is because - there are a lot of calculation needed for PHY      - ECC are interleaved with data (like on marvell-nand or gpmi-nand).
>> >> >>    Therefore:    + RAW mode is complicated    + protecting BBM increases number of lines of source code
>> >> >> - need to support two DMA engines internal and external (slave) We will see on next patch version what is the result.      That page layout looks:
>> >> >
>> >> >Maybe you don't need to support both internal and external DMA?
>> >> >
>> >> >I am pretty sure there are rooms for size reduction.
>> >>
>> >> I describe how it works in general and maybe you help me chose better solution.
>> >>
>> >> HW controller can work in 3 modes. PIO - can work in master or slave DMA
>> >> CDMA - needs Master DMA for accessing command descriptors.
>> >> Generic mode - can use only Slave DMA.
>> >>
>> >> Generic mode is neccessery to implement functions other than page
>> >> program, page read, block erase. So it is essential. I cannot avoid
>> >> to use Slave DMA.
>> >
>> >This deserves a nice comment at the top.
>> Ok I will add the modes description to cover letter. >
>
>Not only to the cover letter: People read the code. Interested people
>might also read the commit log which is quite easy to find. The cover
>letter however will just disappear in the history of the Internet. I
>would rather prefer you explain how the IP works at the top of the
>driver.
So I will add the modes description to both cover letter and 
at the top of the driver. 
>
>
>Thanks,
>Miquèl

Thanks,
Piotr