typo in Documentation/devices.txt ?

typo in Documentation/devices.txt ?

[허종만]

Hi, all..

Here is description for MMC block devices in Documentation/devices.txt :

    179 block       MMC block devices
                      0 = /dev/mmcblk0      First SD/MMC card
                      1 = /dev/mmcblk0p1    First partition on first MMC card
                      8 = /dev/mmcblk1      Second SD/MMC card
                      ^^^^^^^^^^^^^^^^^^
                    The start of next SD/MMC card can be configured with
                    CONFIG_MMC_BLOCK_MINORS, or overridden at boot/modprobe
                    time using the mmcblk.perdev_minors option. That would
                    bump the offset between each card to be the configured
                    value instead of the default 8.


Shouldn't  "8 = /dev/mmcblk1" be "9 = /dev/mmcblk1" ?

If we have 8 partitions on first MMC card, we need mmcblk0p1 ~ mmcblk0p8 devices, with minor number 1 ~ 8.
Am I misunderstanding?

Regards,
Jongman Heo.

Re: typo in Documentation/devices.txt ?

[Aaron Lu]

Hi,

On Thu, Jan 05, 2012 at 07:08:27AM +0000, 허종만 wrote:
> 
> Hi, all..
> 
> Here is description for MMC block devices in Documentation/devices.txt :
> 
>     179 block       MMC block devices
>                       0 = /dev/mmcblk0      First SD/MMC card
>                       1 = /dev/mmcblk0p1    First partition on first MMC card
>                       8 = /dev/mmcblk1      Second SD/MMC card
>                       ^^^^^^^^^^^^^^^^^^
>                     The start of next SD/MMC card can be configured with
>                     CONFIG_MMC_BLOCK_MINORS, or overridden at boot/modprobe
>                     time using the mmcblk.perdev_minors option. That would
>                     bump the offset between each card to be the configured
>                     value instead of the default 8.
> 
> 
> Shouldn't  "8 = /dev/mmcblk1" be "9 = /dev/mmcblk1" ?

No, mmcblk1's minor is 8, mmcblk2's minor is 16, etc...

> 
> If we have 8 partitions on first MMC card, we need mmcblk0p1 ~ mmcblk0p8 devices, with minor number 1 ~ 8.
> Am I misunderstanding?

Each mmc block device by default has 8 minors, not 8 partitions. Minor 0
represent the whole disk. So each mmc block device at most has 7
partitions instead of 8.

See code in function mmc_blk_alloc_req on assigning minor value to the
whole disk of the block device:
md->disk->first_minor = devidx * perdev_minors;

And code in function blk_alloc_devt on checking partition number against
disk minors:
	/* in consecutive minor range? */
	if (part->partno < disk->minors) {
		*devt = MKDEV(disk->major, disk->first_minor + part->partno);
		return 0;
	}

-Aaron

> 
> Regards,
> Jongman Heo.