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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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