linux-kernel - Re: [PATCH 2/8] mtd: rawnand: Let callers use the bare Hamming helpers

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Message-Id: <20211015103313.950354-1-miquel.raynal@bootlin.com>
Date:   Fri, 15 Oct 2021 12:33:13 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>
Cc:     linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Vladimir Zapolskiy <vz@...ia.com>
Subject: Re: [PATCH 2/8] mtd: rawnand: Let callers use the bare Hamming helpers

On Tue, 2021-09-28 at 22:15:01 UTC, Miquel Raynal wrote:
> Before the introduction of the ECC framework infrastructure, many
> drivers used the ->calculate/correct() Hamming helpers directly. The
> point of this framework was to avoid this kind of hackish calls and use a
> proper and generic API but it is true that in certain cases, drivers
> still need to use these helpers in order to do ECC computations on
> behalf of their limited hardware.
> 
> Right after the introduction of the ECC engine core introduction, it was
> spotted that it was not possible to use the shiny rawnand software ECC
> helpers so easily because an ECC engine object should have been
> allocated and initialized first. While this works well in most cases,
> for these drivers just leveraging the power of a single helper in
> conjunction with some pretty old and limited hardware, it did not fit.
> 
> The idea back then was to declare intermediate helpers which would make
> use of the exported software ECC engine bare functions while keeping the
> rawnand layer compatibility. As there was already functions with the
> rawnand_sw_hamming_ prefix it was decided to declare new local helpers
> for this purpose in each driver needing one.
> 
> Besides being far from optimal, this design choice was blamed by Linus
> when he pulled the "fixes" pull request [1] so that is why now it is
> time to clean this mess up.
> 
> Enhancing the implementation of the rawnand_ecc_sw_* helpers to support
> both cases, when the ECC object is instantiated and when it is not is a
> quite elegant way to solve this situation. This way, we can still use
> the existing and exported rawnand helpers while avoiding the need for
> each driver to declare its own helper.
> 
> Following this change, most of the fixes sent in [2] can now be safely
> reverted. Only the fsmc fix will need to be kept because there is
> actually something specific to the driver to do in its ->correct()
> helper.
> 
> [1] https://lore.kernel.org/lkml/CAHk-=wh_ZHF685Fni8V9is17mj=pFisUaZ_0=gq6nbK+ZcyQmg@mail.gmail.com/
> [2] https://lore.kernel.org/linux-mtd/20210413161840.345208-1-miquel.raynal@bootlin.com/
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next.

Miquel