linux-kernel - Re: [PATCH v6 2/7] mmc: block: Add mmc_bdev_to

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Message-ID: <7bddacf1-5fe0-5119-48ac-6a0cc65c5af0@gmail.com>
Date:   Mon, 18 May 2020 02:55:30 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>,
        Stephen Warren <swarren@...dotorg.org>,
        Nicolas Chauvet <kwizart@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Billy Laws <blaws05@...il.com>,
        Nils Östlund <nils@...tan.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-tegra@...r.kernel.org, linux-block@...r.kernel.org,
        Andrey Danin <danindrey@...l.ru>,
        Gilles Grandou <gilles@...ndou.net>,
        Ryan Grachek <ryan@...ted.us>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Steve McIntyre <steve@...val.com>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH v6 2/7] mmc: block: Add mmc_bdev_to_card() helper

17.05.2020 05:12, Dmitry Osipenko пишет:
> NVIDIA Tegra Partition Table takes into account MMC card's BOOT_SIZE_MULT
> parameter, and thus, the partition parser needs to retrieve that EXT_CSD
> value from the block device.  There are also some other parts of struct
> mmc_card that are needed for the partition parser in order to calculate
> the eMMC offset and verify different things.  This patch introduces new
> helper which takes block device for the input argument and returns the
> corresponding MMC card.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/mmc/core/block.c   | 15 +++++++++++++++
>  include/linux/mmc/blkdev.h | 13 +++++++++++++
>  2 files changed, 28 insertions(+)
>  create mode 100644 include/linux/mmc/blkdev.h
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index c5367e2c8487..99298e888381 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -40,6 +40,7 @@
>  #include <linux/debugfs.h>
>  
>  #include <linux/mmc/ioctl.h>
> +#include <linux/mmc/blkdev.h>
>  #include <linux/mmc/card.h>
>  #include <linux/mmc/host.h>
>  #include <linux/mmc/mmc.h>
> @@ -305,6 +306,20 @@ static ssize_t force_ro_store(struct device *dev, struct device_attribute *attr,
>  	return ret;
>  }
>  
> +struct mmc_card *mmc_bdev_to_card(struct block_device *bdev)
> +{
> +	struct mmc_blk_data *md;
> +
> +	if (bdev->bd_disk->major != MMC_BLOCK_MAJOR)
> +		return NULL;
> +
> +	md = mmc_blk_get(bdev->bd_disk);
> +	if (!md)
> +		return NULL;
> +
> +	return md->queue.card;
> +}
> +
>  static int mmc_blk_open(struct block_device *bdev, fmode_t mode)
>  {
>  	struct mmc_blk_data *md = mmc_blk_get(bdev->bd_disk);
> diff --git a/include/linux/mmc/blkdev.h b/include/linux/mmc/blkdev.h
> new file mode 100644
> index 000000000000..67608c58de70
> --- /dev/null
> +++ b/include/linux/mmc/blkdev.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + *  linux/include/linux/mmc/blkdev.h
> + */
> +#ifndef LINUX_MMC_BLOCK_DEVICE_H
> +#define LINUX_MMC_BLOCK_DEVICE_H
> +
> +struct block_device;
> +struct mmc_card;
> +
> +struct mmc_card *mmc_bdev_to_card(struct block_device *bdev);
> +
> +#endif /* LINUX_MMC_BLOCK_DEVICE_H */
> 

Hello Ulf / Jens and everyone,

Guys, what do you think about this change?

Currently it's not allowed to compile MMC_BLOCK as a loadable kernel
module if TEGRA_PARTITION is enabled because it depends on MMC_BLOCK
presence. I'm curious if this situation could be improved by moving
mmc_bdev_to_card() to linux/mmc/blkdev.h and then:

1. Moving all private mmc/core/block.c structs to the public
linux/mmc/blkdev.h.

2. Or adding a "private opaque" pointer to a struct block_device and
setting it to md->queue.card, for example.

3. I see that struct block_device already has some bd_private field, but
I'm not sure whether it could be used for what I'm trying to achieve.
Actually I don't see where bd_private is used in kernel at all.

I'd like get yours feedback, thanks in advance.