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