From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Tue, 5 Dec 2017 11:28:15 +0100
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Kamal Dasu <kdasu.kdev@gmail.com>, Richard Weinberger <richard@nod.at>,
 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Broadcom Kernel
 Feedback List <bcm-kernel-feedback-list@broadcom.com>, Marek Vasut
 <marek.vasut@gmail.com>, Chen-Yu Tsai <wens@csie.org>, linux-mtd
 <linux-mtd@lists.infradead.org>, Cyrille Pitchen
 <cyrille.pitchen@wedev4u.fr>, Han Xu <han.xu@nxp.com>, Maxime Ripard
 <maxime.ripard@free-electrons.com>, Brian Norris
 <computersforpeace@gmail.com>, David Woodhouse <dwmw2@infradead.org>,
 linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] mtd: nand: squash struct nand_buffers into struct
 nand_chip
Message-ID: <20171205112815.0b59ab2d@bbrezillon>
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On Tue, 5 Dec 2017 19:02:26 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> Hi Boris,
> 
> 2017-12-04 18:10 GMT+09:00 Boris Brezillon
> <boris.brezillon@free-electrons.com>:
> 
> >>       }
> >>
> >>       if (!(chip->options & NAND_OWN_BUFFERS)) {
> >> -             nbuf = kzalloc(sizeof(*nbuf), GFP_KERNEL);
> >> -             if (!nbuf)
> >> +             chip->ecccalc = kmalloc(mtd->oobsize, GFP_KERNEL);
> >> +             if (!chip->ecccalc)
> >>                       return -ENOMEM;
> >>
> >> -             nbuf->ecccalc = kmalloc(mtd->oobsize, GFP_KERNEL);
> >> -             if (!nbuf->ecccalc) {
> >> +             chip->ecccode = kmalloc(mtd->oobsize, GFP_KERNEL);
> >> +             if (!chip->ecccode) {
> >>                       ret = -ENOMEM;
> >>                       goto err_free_nbuf;
> >>               }  
> >
> > Hm, again not directly related to this patch, but I wonder if we
> > couldn't allocate those buffers only when they are really needed.
> > For example, most NAND controllers do the ECC calculation/correct
> > in HW and simply don't need those buffers.  
> 
> 
> The only idea I came up with is to add a new flag,
> but I am not sure if you are happy with it
> because we are removing NAND_OWN_BUFFERS.

All drivers using ->calc/code_buf are providing a ->correct() and/or
->calculate() method, so I thought we could make the allocation
dependent on the presence of one of these hooks [1].

The only exception is the denali driver, but I think we can patch it
to not use the ->code_buf buffer [2].

[1]http://code.bulix.org/2ks7yp-236649
[2]http://code.bulix.org/sxqx7o-236650