mmc: core: Allow hosts to specify non-support for MMC commands

Host drivers which needs to valdiate for non-supported MMC
commands and returnn error code for such requests.

To improve and simplify the behaviour, let's invent MMC_CAP2_NO_MMC
which these host drivers can set to tell the mmc core to skip sending MMC
commands during card initialization.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/core.c

@@ -2510,8 +2510,9 @@ static int mmc_rescan_try_freq(struct mmc_host *host, unsigned freq)
 		if (!mmc_attach_sd(host))
 			return 0;
 
-	if (!mmc_attach_mmc(host))
-		return 0;
+	if (!(host->caps2 & MMC_CAP2_NO_MMC))
+		if (!mmc_attach_mmc(host))
+			return 0;
 
 	mmc_power_off(host);
 	return -EIO;

include/linux/mmc/host.h

@@ -310,6 +310,7 @@ struct mmc_host {
 #define MMC_CAP2_NO_SDIO	(1 << 19)	/* Do not send SDIO commands during initialization */
 #define MMC_CAP2_HS400_ES	(1 << 20)	/* Host supports enhanced strobe */
 #define MMC_CAP2_NO_SD		(1 << 21)	/* Do not send SD commands during initialization */
+#define MMC_CAP2_NO_MMC		(1 << 22)	/* Do not send (e)MMC commands during initialization */
 
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */