linux-kernel - Re: [PATCH v2] mtd: rawnand: denali: do not pass zero maxchips to nand

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Message-ID: <20180827092341.1385ea7d@bbrezillon>
Date:   Mon, 27 Aug 2018 09:23:41 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2] mtd: rawnand: denali: do not pass zero maxchips to
 nand_scan()

On Mon, 27 Aug 2018 16:01:41 +0900
Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident()
> if maxchips is zero") gave a new meaning for calling nand_scan_ident()
> with maxchips=0.
> 
> It is a special usage for some drivers such as docg4, but actually
> the Denali driver may pass maxchips=0 to nand_scan() when the driver
> is enabled but no NAND chip is found on the board for some reasons.
> 
> If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident()
> is skipped, then nand_set_defaults() is skipped as well.  Thus, the
> driver must set chip->controller beforehand.  Otherwise, nand_attach()
> causes NULL pointer dereference.
> 
> In fact, the Denali controller knows the number of connected chips
> before calling nand_scan_ident(); if DEVICE_RESET fails, there is no
> chip in that chip select.  Then, denali_reset_banks() sets the maxchips
> to the number of detected chips.  If no chip is found, maxchips is zero.
> 
> In this case, there is no point for calling nand_scan() because we know
> it will fail for sure.  Let's make the probe function fail immediately.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Looks good to me. I'm waiting for Miquel's ack and I'll queue it to
mtd/fixes.

Thanks,

Boris