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

Adrian Hunter
2009-07-25T16:16:56Z

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);
+