linux-kernel - Re: [PATCH 01/27] mtd: nand: introduce function to fix a common bug in most nand-drivers not showing a device in sysfs

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Message-ID: <20141102210353.GA9968@gmail.com>
Date:	Sun, 2 Nov 2014 22:03:53 +0100
From:	Frans Klaver <fransklaver@...il.com>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	Alexander Holler <holler@...oftware.de>,
	linux-kernel@...r.kernel.org, linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 01/27] mtd: nand: introduce function to fix a common bug
 in most nand-drivers not showing a device in sysfs

On Wed, May 28, 2014 at 01:43:44AM -0700, Brian Norris wrote:
> And in fact, if any drivers are missing mtd->name, perhaps it's best to
> just modify the MTD registration to give them a default:
> 
> 	if (!mtd->name)
> 		mtd->name = dev_name(&pdev->dev);
> 

...

> How about we rethink the "helper" approach, and instead just do
> validation in the core code? This would cover most of the important
> parts of your helper, I think:
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index d201feeb3ca6..39ba5812a5a3 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -397,6 +397,11 @@ int add_mtd_device(struct mtd_info *mtd)
>  	if (device_register(&mtd->dev) != 0)
>  		goto fail_added;
>  
> +	if (mtd->dev.parent)
> +		mtd->owner = mtd->dev.parent->driver->owner;
> +	else
> +		WARN_ON(1);
> +

So I've picked this up now. I do largely agree with the suggested
approach where the validation and default settings are done in the core
code. There is a problem with this, though. There are MTD devices that
call mtd_device_parse_register() in the _init() function (such as the
maps drivers). These don't have a device ready to be used as parent, and
they would always be throwing this warning.

So either not having a parent device is bad, or it isn't. The comment
suggests it is, the existing code suggests it isn't. So we'll need to
make a decision about who's right.

>  	if (MTD_DEVT(i))
>  		device_create(&mtd_class, mtd->dev.parent,
>  			      MTD_DEVT(i) + 1,
> diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
> index 1ca9aec141ff..9869bbef50cf 100644
> --- a/drivers/mtd/mtdpart.c
> +++ b/drivers/mtd/mtdpart.c
> @@ -370,7 +370,6 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
>  	slave->mtd.subpage_sft = master->subpage_sft;
>  
>  	slave->mtd.name = name;
> -	slave->mtd.owner = master->owner;

What would be the purpose of removing this line? Owner is already set?
Can we rely on that?

Thanks,
Frans
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