linux-kernel - Re: [PATCH 7/32] mmc: add host capabilities for SD only and MMC only

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Date:	Sat, 25 Jul 2009 16:53:36 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Adrian Hunter <adrian.hunter@...ia.com>
Cc:	Pierre Ossman <pierre@...man.eu>,
	Jarkko Lavinen <jarkko.lavinen@...ia.com>,
	Denis Karpov <ext-denis.2.karpov@...ia.com>,
	linux-omap Mailing List <linux-omap@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 7/32] mmc: add host capabilities for SD only and MMC
	only

On Fri, Jul 10, 2009 at 03:40:54PM +0300, Adrian Hunter wrote:
> 
> Some hosts can accept only certain types of cards.
> For example, an eMMC is MMC only and a uSD slot may
> be SD only.  However the MMC card scanning logic
> checks for all card types one by one.
> 
> Add host capabilities to specify which card types
> cannot be used, and amend the card scanning logic
> to skip scanning for those types.
> 

I'm only nitpicking here, but I think that logic is a little inverted.
By saying which cards cannot be used (as opposed to which cards can be
used), we get conditionals like this,

>  
> -	mmc_send_if_cond(host, host->ocr_avail);
> +	if (!(host->caps & MMC_CAP_NOT_SDIO) || !(host->caps & MMC_CAP_NOT_SD))
> +		mmc_send_if_cond(host, host->ocr_avail);
> +

Whilst reviewing this patch it took my brain a few too many seconds to
parse that as "if the host is capable of SDIO or SD".


> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 0a60b02..e996967 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -150,6 +150,13 @@ struct mmc_host {
>  #define MMC_CAP_DISABLE		(1 << 7)	/* Can the host be disabled */
>  #define MMC_CAP_NONREMOVABLE	(1 << 8)	/* Nonremovable e.g. eMMC */
>  #define MMC_CAP_WAIT_WHILE_BUSY	(1 << 9)	/* Waits while card is busy */
> +#define MMC_CAP_NOT_SDIO	(1 << 10)	/* Card cannot be SDIO */
> +#define MMC_CAP_NOT_SD		(1 << 11)	/* Card cannot be SD */
> +#define MMC_CAP_NOT_MMC		(1 << 12)	/* Card cannot be MMC */
> +
> +#define MMC_CAP_SDIO_ONLY	(MMC_CAP_NOT_SD | MMC_CAP_NOT_MMC)
> +#define MMC_CAP_SD_ONLY		(MMC_CAP_NOT_SDIO | MMC_CAP_NOT_MMC)
> +#define MMC_CAP_MMC_ONLY	(MMC_CAP_NOT_SDIO | MMC_CAP_NOT_SD)
>  

And by saying what capabilities a host supports, when we add new
capabilities we don't have to modify existing code to say that it
doesn't support the new capability.
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