mmc: core: Add a new quirk for limiting clock rate

This patch adds a quirk to limit clock rate which
can be used to reduce the SDIO clock rate for some
chips with broken UHS.

Signed-off-by: Harish Jenny K N <[e-mail]>
Reviewed-by: Shawn Lin <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/card.h

···
 	card->quirks &= ~data;
 }
 
+static inline void __maybe_unused add_limit_rate_quirk(struct mmc_card *card,
+						       int data)
+{
+	card->quirk_max_rate = data;
+}
+
 /*
  * Quirk add/remove for MMC products.
  */

drivers/mmc/core/sdio.c

···
 	unsigned int bus_speed, timing;
 	int err;
 	unsigned char speed;
+	unsigned int max_rate;
 
 	/*
 	 * If the host doesn't support any of the UHS-I modes, fallback on
···
 	if (err)
 		return err;
 
+	max_rate = min_not_zero(card->quirk_max_rate,
+				card->sw_caps.uhs_max_dtr);
+
 	if (bus_speed) {
 		mmc_set_timing(card->host, timing);
-		mmc_set_clock(card->host, card->sw_caps.uhs_max_dtr);
+		mmc_set_clock(card->host, max_rate);
 	}
 
 	return 0;

include/linux/mmc/card.h

···
 #define MMC_TYPE_SD_COMBO	3		/* SD combo (IO+mem) card */
 	unsigned int		state;		/* (our) card state */
 	unsigned int		quirks; 	/* card quirks */
+	unsigned int		quirk_max_rate;	/* max rate set by quirks */
 #define MMC_QUIRK_LENIENT_FN0	(1<<0)		/* allow SDIO FN0 writes outside of the VS CCCR range */
 #define MMC_QUIRK_BLKSZ_FOR_BYTE_MODE (1<<1)	/* use func->cur_blksize */
 						/* for byte mode */