linux-kernel - Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block devices

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Message-ID: <561CA8D3.2090507@ti.com>
Date:	Tue, 13 Oct 2015 12:16:43 +0530
From:	Lokesh Vutla <a0131933@...com>
To:	Heiko Schocher <hs@...x.de>, <linux-kernel@...r.kernel.org>
CC:	Arnd Bergmann <arnd@...db.de>, <linux-mmc@...r.kernel.org>,
	Dirk Behme <dirk.behme@...ch.com>, <Georg.Soffel@...ch-si.com>,
	<linux-omap@...r.kernel.org>, Ulf Hansson <ulf.hansson@...aro.org>,
	"Menon, Nishanth" <nm@...com>
Subject: Re: [PATCH] mmc: omap_hsmmc: fix initialization order of mmc block
 devices

+Nishanth,

On Tuesday 13 October 2015 10:59 AM, Heiko Schocher wrote:
> On embedded devices, often there is a combination of
> removable mmc devices (e.g. MMC/SD cards) and hard
> wired ones (e.g. eMMC). Depending on the hardware
> configuration, the 'mmcblkN' node might change if
> the removable device is available or not at boot time.
> 
> E.g. if the removable device is attached at boot time,
> it might become mmxblk0. And the hard wired one mmcblk1.
> But if the removable device isn't there at boot time,
> the hard wired one will become mmcblk0. This makes it
> somehow difficult to hard code the root device to the
> non-removable device and boot fast.

Why not use "root=PARTUUID=${uuid}" option instead of relying on mmcblk no?
U-Boot can easily detect your partuuid. Refer to [1] on how TI platforms
does this in u-boot.

[1]
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=437bc42e7ff930dc4d4bd47199d2e823cf84bf4c;hp=85d17be374678ec37fd1e55db994a942e400dc80

Thanks and regards,
Lokesh
> 
> Signed-off-by: Heiko Schocher <hs@...x.de>
> ---
> Dirk Behme tried to bring this in, last mail I found:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-July/111022.html
> where Dirk worked in Arnds suggestion to use the
> "/aliases" device node"
> 
> I adapt this to the omap_hsmmc driver.
> 
> Is there another solution for this problem?
> Or why was this patch not accepted to mainline?
> 
>  drivers/mmc/card/block.c      | 6 ++++--
>  drivers/mmc/host/omap_hsmmc.c | 6 ++++++
>  include/linux/mmc/host.h      | 3 +++
>  3 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index c742cfd..62250d8 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -2106,7 +2106,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  	struct mmc_blk_data *md;
>  	int devidx, ret;
>  
> -	devidx = find_first_zero_bit(dev_use, max_devices);
> +	devidx = find_next_zero_bit(dev_use, max_devices,
> +				    card->host->devidx);
>  	if (devidx >= max_devices)
>  		return ERR_PTR(-ENOSPC);
>  	__set_bit(devidx, dev_use);
> @@ -2124,7 +2125,8 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  	 * index anymore so we keep track of a name index.
>  	 */
>  	if (!subname) {
> -		md->name_idx = find_first_zero_bit(name_use, max_devices);
> +		md->name_idx = find_next_zero_bit(name_use, max_devices,
> +						  card->host->devidx);
>  		__set_bit(md->name_idx, name_use);
>  	} else
>  		md->name_idx = ((struct mmc_blk_data *)
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index 7fb0753..0b45b48 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2059,6 +2059,12 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
>  	host->pbias_enabled = 0;
>  	host->vqmmc_enabled = 0;
>  
> +	if (pdev->dev.of_node) {
> +		ret = of_alias_get_id(pdev->dev.of_node, "mmcblk");
> +		if (ret >= 0)
> +			host->mmc->devidx = ret;
> +	}
> +
>  	ret = omap_hsmmc_gpio_init(mmc, host, pdata);
>  	if (ret)
>  		goto err_gpio;
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 83b81fd..4f071681 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -382,6 +382,9 @@ struct mmc_host {
>  	int			dsr_req;	/* DSR value is valid */
>  	u32			dsr;	/* optional driver stage (DSR) value */
>  
> +	/* preferred mmc block device index (mmcblkX) */
> +	unsigned int		devidx;
> +
>  	unsigned long		private[0] ____cacheline_aligned;
>  };
>  
> 
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