linux-kernel - Re: [PATCH v2 20/53] mtd: nand: denali: do not set mtd->name

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Date:   Wed, 29 Mar 2017 20:30:54 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     linux-mtd@...ts.infradead.org,
        Laurent Monat <laurent.monat@...uantique.com>,
        thorsten.christiansson@...uantique.com,
        Enrico Jorns <ejo@...gutronix.de>,
        Jason Roberts <jason.e.roberts@...el.com>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Brian Norris <computersforpeace@...il.com>,
        Graham Moore <grmoore@...nsource.altera.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Chuanxiao Dong <chuanxiao.dong@...el.com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>
Subject: Re: [PATCH v2 20/53] mtd: nand: denali: do not set mtd->name

Hi Boris,


2017-03-29 16:19 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> On Wed, 29 Mar 2017 10:19:02 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>> Hi Boris,
>>
>> 2017-03-29 6:40 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
>> > On Wed, 29 Mar 2017 06:32:24 +0900
>> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>> >
>> >> Hi Boris,
>> >>
>> >> 2017-03-28 0:31 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
>> >> > On Wed, 22 Mar 2017 23:07:27 +0900
>> >> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>> >> >
>> >> >> This will be filled by nand_scan_ident() later.
>> >> >>
>> >> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> >> >> ---
>> >> >>
>> >> >> Changes in v2: None
>> >> >>
>> >> >>  drivers/mtd/nand/denali.c | 1 -
>> >> >>  1 file changed, 1 deletion(-)
>> >> >>
>> >> >> diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
>> >> >> index 3badb1d..1706975 100644
>> >> >> --- a/drivers/mtd/nand/denali.c
>> >> >> +++ b/drivers/mtd/nand/denali.c
>> >> >> @@ -1495,7 +1495,6 @@ int denali_init(struct denali_nand_info *denali)
>> >> >>
>> >> >>       /* now that our ISR is registered, we can enable interrupts */
>> >> >>       denali_set_intr_modes(denali, true);
>> >> >> -     mtd->name = "denali-nand";
>> >> >
>> >> > Are you sure this is safe to do that? When mtd->name is NULL, the core
>> >> > takes the parent name, and in the denali_dt case it's not "denali-nand",
>> >> > which means you're breaking mtdparts compat.
>> >>
>> >> How big impact is this?
>> >
>> > Breaking boot on some platforms (those defining partitions through
>> > mtdparts= cmdline parameter), which is not negligible :P.
>> >
>> >>
>> >> I think a bootloader could give mtdparts=denali-nand:...
>> >> but, now we are able to have partitions in DT nodes.
>> >
>> > Just because you have a new way to describe partitions (using DT) does
>> > not mean people are not using the old one (mtdparts= parameter).
>>
>>
>> I thought DT-node derived name can identify the hardware
>> even if multiple Denali controllers exist on an SoC.
>>
>> Anyway, I admit this is a kind of breakage.
>>
>> If this one is reject, I will drop it drop v3.
>>
>
> Yes, please keep the existing name, changing that without extra
> precautions has proven to be a bad idea [1].
>
> Note that we now have a way to give user-friendly names to MTD devices
> through DT definitions [2]. So, if you ever want to assing a specific
> name to your NAND, all you have to do is add a label property to the
> NAND device node, and then, in the driver:
>
>         nand_set_flash_node(chip, denali->dev->of_node);
>
>         /*
>          * Fallback to the default name if no label property was
>          * defined.
>          */
>         if (!mtd->name)
>                 mtd->name = "denali-nand";
>
>
> [1]https://patchwork.ozlabs.org/patch/707065/

I will replace it with this solution.
Thanks for the tip!



-- 
Best Regards
Masahiro Yamada