mmc: core: Parse and use the new max-sd-hs-hz DT property

Introduce a new device tree flag to cap the maximum High-Speed (HS)
mode frequency for SD cards, accommodating board-specific
electrical limitations which cannot support the default 50Mhz HS
frequency and others.

Signed-off-by: Sarthak Garg <[email protected]>
Signed-off-by: Ulf Hansson <[email protected]>

Author: Sarthak Garg

drivers/mmc/core/host.c

@@ -302,6 +302,8 @@ int mmc_of_parse(struct mmc_host *host)
 	/* f_max is obtained from the optional "max-frequency" property */
 	device_property_read_u32(dev, "max-frequency", &host->f_max);
 
+	device_property_read_u32(dev, "max-sd-hs-hz", &host->max_sd_hs_hz);
+
 	/*
 	 * Configure CD and WP pins. They are both by default active low to
 	 * match the SDHCI spec. If GPIOs are provided for CD and / or WP, the

drivers/mmc/core/sd.c

@@ -359,7 +359,7 @@ static int mmc_read_switch(struct mmc_card *card)
 	}
 
 	if (status[13] & SD_MODE_HIGH_SPEED)
-		card->sw_caps.hs_max_dtr = HIGH_SPEED_MAX_DTR;
+		card->sw_caps.hs_max_dtr = card->host->max_sd_hs_hz ?: HIGH_SPEED_MAX_DTR;
 
 	if (card->scr.sda_spec3) {
 		card->sw_caps.sd3_bus_mode = status[13];

include/linux/mmc/host.h

@@ -576,6 +576,7 @@ struct mmc_host {
 	int			hsq_depth;
 
 	u32			err_stats[MMC_ERR_MAX];
+	u32			max_sd_hs_hz;
 	unsigned long		private[] ____cacheline_aligned;
 };