Re: Dynamic MMC device naming vs. bootloaders

[Kishore Kadiyala <kishorek.kadiyala@gmail.com>]

Hi Stephen,

On Mon, Apr 4, 2011 at 11:09 PM, Stephen Warren <swarren@nvidia.com> wrote:
> Chris et. al.,
>
> I'm working on an ARM system that contains at least two MMC/SD devices;
> specifically the board has an internal MMC device, and an SD card slot,
> although the SoC has four MMC/SD hosts IIRC.
>
> The kernel's naming of these devices is dynamic. If the SD card is not
> plugged in, the internal MMC is always known as mmcblock0. If the SD card
> is plugged in too, sometimes the internal MMC is mmcblk0 and sometimes it's
> mmcblk1. I assume this is timing related; 2.6.37 usually seemed to name
> them "in order", whereas 2.6.38 usually seems to name them "backwards".
>
> This causes problems with the bootloader scripts I'm using, which assumes
> that the internal MMC is always device 0 and the SD slot is always device 1,
> and hence provides kernel command-line argument root=/dev/mmcblk0p3 or
> root=/dev/mmcblk1p3 based on whether it booted from SD or internal MMC (SD
> is searched for a valid image first by the bootloader).

Just follow this thread which discusses the same but for OMAP4 controller
http://www.mail-archive.com/linux-omap@vger.kernel.org/msg47853.html

One solution could be make your internal MMC always registered as
mmcblk0 and the
removable one as next device.

Regards,
Kishore
>
> This could be solved by naming the kernel MMC devices statically based on
> the host controller, rather than dynamically based on the first available
> ID when the actual storage is detected. The patch below implements this.
>
> Is this patch conceptually acceptable for the MMC driver? Obviously, a
> complete patch would need to also remove the dev_use structure etc.
>
> Another solution might be for the kernel command-line to specify the
> filesystem UUID, rather than a device node. However, this entails much more
> work for the bootloader. I'm not sure whether U-Boot can do this right now?
> And actually, the filesystem images I'm using don't always have a UUID by
> dDefault IIRC.
>
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index bfc8a8a..5131b02 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -581,7 +581,7 @@ static struct mmc_blk_data *mmc_blk_alloc(struct mmc_card *card)
>        struct mmc_blk_data *md;
>        int devidx, ret;
>
> -       devidx = find_first_zero_bit(dev_use, max_devices);
> +       devidx = card->host->index;
>        if (devidx >= max_devices)
>                return ERR_PTR(-ENOSPC);
>        __set_bit(devidx, dev_use);
>
> Thanks for any feedback.
>
> --
> nvpublic
>
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