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SubjectRe: [PATCH] mmc: make number of mmcblk minors configurable
On Tue, 17 Aug 2010 23:13:33 -0500
Olof Johansson <olof@lixom.net> wrote:

> The old limit of number of minor numbers per mmcblk device was hardcoded
> at 8. This isn't enough for some of the more elaborate partitioning
> schemes, for example those used by Chrome OS.
>
> Since there might be a bunch of systems out there with static /dev
> contents that relies on the old numbering scheme, let's make it a
> build-time option with the default set to the previous 8.
>

How does the numbering scheme change? What's the user-visible effect
of setting CONFIG_MMC_BLOCK_MINORS to, say, 16?

> ---
> drivers/mmc/card/Kconfig | 10 ++++++++++
> drivers/mmc/card/block.c | 20 ++++++++------------
> 2 files changed, 18 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/mmc/card/Kconfig b/drivers/mmc/card/Kconfig
> index 3f2a912..e939dcf 100644
> --- a/drivers/mmc/card/Kconfig
> +++ b/drivers/mmc/card/Kconfig
> @@ -14,6 +14,16 @@ config MMC_BLOCK
> mount the filesystem. Almost everyone wishing MMC support
> should say Y or M here.
>
> +config MMC_BLOCK_MINORS
> + int "Number of minors per block device"
> + range 4 32
> + default 8
> + help
> + Number of minors per block device. One is needed for every
> + partition (plus one for the whole device).
> + Default is 8 to be backwards compatible with previous
> + hardcoded device numbering.

If possible it would be better to do this with a kernel boot (or
modprobe) parameter. That permits vendors to ship packaged kernels
with full functionality, etc. Possible? The default value of the
runtime-settable parameter could be Kconfigurable is there's a real
need for that.


> config MMC_BLOCK_BOUNCE
> bool "Use bounce buffer for simple hosts"
> depends on MMC_BLOCK
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index d545f79..524e232 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -45,13 +45,9 @@
>
> MODULE_ALIAS("mmc:block");
>
> -/*
> - * max 8 partitions per card
> - */
> -#define MMC_SHIFT 3
> -#define MMC_NUM_MINORS (256 >> MMC_SHIFT)
> +#define MMC_MAX_DEVICES ((255 + CONFIG_MMC_BLOCK_MINORS) / CONFIG_MMC_BLOCK_MINORS)

So if I increase CONFIG_MMC_BLOCK_MINORS, I can no longer support as
many devices? That'd be worth mentioning somewhere?

fwiw, the above could use DIV_ROUND_UP().




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