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

[Adrian Hunter]

Matt Fleming wrote:
> 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.

If the capabilities are the other way around, then all existing drivers
must be changed.  On the other hand, the if statement can easily be
improved:

#define mmc_cap_mmc(host) (!((host)->caps & MMC_CAP_NOT_MMC))
#define mmc_cap_sd(host) (!((host)->caps & MMC_CAP_NOT_SD))
#define mmc_cap_sdio(host) (!((host)->caps & MMC_CAP_NOT_SDIO))

-	mmc_send_if_cond(host, host->ocr_avail);
+	if (mmc_cap_sdio(host) || mmc_cap_sd(host))
+		mmc_send_if_cond(host, host->ocr_avail);
+
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