mmc: bcm2835-host: let firmware manage the clock divisor

Newer firmware can manage the SDCDIV clock divisor register, allowing
the divisor to scale with the core as necessary.

Leverage this ability if the firmware supports it.

Adapted from the following raspberrypi Linux kernel commit:

  bcm2835-sdhost: Firmware manages the clock divisor
  08532d242d

Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>

arch/arm/mach-bcm283x/include/mach/mbox.h

@@ -252,6 +252,22 @@ struct bcm2835_mbox_tag_get_clock_rate {
 	} body;
 };
 
+#define BCM2835_MBOX_TAG_SET_SDHOST_CLOCK	0x00038042
+
+struct bcm2835_mbox_tag_set_sdhost_clock {
+	struct bcm2835_mbox_tag_hdr tag_hdr;
+	union {
+		struct {
+			u32 rate_hz;
+		} req;
+		struct {
+			u32 rate_hz;
+			u32 rate_1;
+			u32 rate_2;
+		} resp;
+	} body;
+};
+
 #define BCM2835_MBOX_TAG_ALLOCATE_BUFFER	0x00040001
 
 struct bcm2835_mbox_tag_allocate_buffer {

arch/arm/mach-bcm283x/include/mach/msg.h

@@ -22,6 +22,16 @@ int bcm2835_power_on_module(u32 module);
  */
 int bcm2835_get_mmc_clock(u32 clock_id);
 
+/**
+ * bcm2835_set_sdhost_clock() - determine if firmware controls sdhost cdiv
+ *
+ * @rate_hz: Input clock frequency
+ * @rate_1: Returns a clock frequency
+ * @rate_2: Returns a clock frequency
+ * @return 0 of OK, -EIO on error
+ */
+int bcm2835_set_sdhost_clock(u32 rate_hz, u32 *rate_1, u32 *rate_2);
+
 /**
  * bcm2835_get_video_size() - get the current display size
  *

arch/arm/mach-bcm283x/msg.c

@@ -21,6 +21,12 @@ struct msg_get_clock_rate {
 	u32 end_tag;
 };
 
+struct msg_set_sdhost_clock {
+	struct bcm2835_mbox_hdr hdr;
+	struct bcm2835_mbox_tag_set_sdhost_clock set_sdhost_clock;
+	u32 end_tag;
+};
+
 struct msg_query {
 	struct bcm2835_mbox_hdr hdr;
 	struct bcm2835_mbox_tag_physical_w_h physical_w_h;
@@ -110,6 +116,28 @@ int bcm2835_get_mmc_clock(u32 clock_id)
 	return clock_rate;
 }
 
+int bcm2835_set_sdhost_clock(u32 rate_hz, u32 *rate_1, u32 *rate_2)
+{
+	ALLOC_CACHE_ALIGN_BUFFER(struct msg_set_sdhost_clock, msg_sdhost_clk, 1);
+	int ret;
+
+	BCM2835_MBOX_INIT_HDR(msg_sdhost_clk);
+	BCM2835_MBOX_INIT_TAG(&msg_sdhost_clk->set_sdhost_clock, SET_SDHOST_CLOCK);
+
+	msg_sdhost_clk->set_sdhost_clock.body.req.rate_hz = rate_hz;
+
+	ret = bcm2835_mbox_call_prop(BCM2835_MBOX_PROP_CHAN, &msg_sdhost_clk->hdr);
+	if (ret) {
+		printf("bcm2835: Could not query sdhost clock rate\n");
+		return -EIO;
+	}
+
+	*rate_1 = msg_sdhost_clk->set_sdhost_clock.body.resp.rate_1;
+	*rate_2 = msg_sdhost_clk->set_sdhost_clock.body.resp.rate_2;
+
+	return 0;
+}
+
 int bcm2835_get_video_size(int *widthp, int *heightp)
 {
 	ALLOC_CACHE_ALIGN_BUFFER(struct msg_query, msg_query, 1);

drivers/mmc/bcm2835_sdhost.c

@@ -181,6 +181,7 @@ struct bcm2835_host {
 	struct udevice		*dev;
 	struct mmc		*mmc;
 	struct bcm2835_plat	*plat;
+	unsigned int		firmware_sets_cdiv:1;
 };
 
 static void bcm2835_dumpregs(struct bcm2835_host *host)
@@ -233,7 +234,7 @@ static void bcm2835_reset_internal(struct bcm2835_host *host)
 	msleep(20);
 	host->clock = 0;
 	writel(host->hcfg, host->ioaddr + SDHCFG);
-	writel(host->cdiv, host->ioaddr + SDCDIV);
+	writel(SDCDIV_MAX_CDIV, host->ioaddr + SDCDIV);
 }
 
 static int bcm2835_wait_transfer_complete(struct bcm2835_host *host)
@@ -598,6 +599,7 @@ static int bcm2835_transmit(struct bcm2835_host *host)
 static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 {
 	int div;
+	u32 clock_rate[2] = { 0 };
 
 	/* The SDCDIV register has 11 bits, and holds (div - 2).  But
 	 * in data mode the max is 50MHz wihout a minimum, and only
@@ -620,6 +622,10 @@ static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 	 * clock divisor at all times.
 	 */
 
+	if (host->firmware_sets_cdiv) {
+		bcm2835_set_sdhost_clock(clock, &clock_rate[0], &clock_rate[1]);
+		clock = max(clock_rate[0], clock_rate[1]);
+	} else {
 		if (clock < 100000) {
 			/* Can't stop the clock, but make it as slow as possible
 			* to show willing
@@ -640,6 +646,10 @@ static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 			div = SDCDIV_MAX_CDIV;
 
 		clock = host->max_clk / (div + 2);
+		host->cdiv = div;
+		writel(host->cdiv, host->ioaddr + SDCDIV);
+	}
+
 	host->mmc->clock = clock;
 
 	/* Calibrate some delays */
@@ -647,9 +657,6 @@ static void bcm2835_set_clock(struct bcm2835_host *host, unsigned int clock)
 	host->ns_per_fifo_word = (1000000000 / clock) *
 		((host->mmc->card_caps & MMC_MODE_4BIT) ? 8 : 32);
 
-	host->cdiv = div;
-	writel(host->cdiv, host->ioaddr + SDCDIV);
-
 	/* Set the timeout to 500ms */
 	writel(host->mmc->clock / 2, host->ioaddr + SDTOUT);
 }
@@ -759,6 +766,7 @@ static int bcm2835_probe(struct udevice *dev)
 	struct bcm2835_host *host = dev_get_priv(dev);
 	struct mmc *mmc = mmc_get_mmc_dev(dev);
 	struct mmc_uclass_priv *upriv = dev_get_uclass_priv(dev);
+	u32 clock_rate[2] = { ~0 };
 
 	host->dev = dev;
 	host->mmc = mmc;
@@ -776,6 +784,9 @@ static int bcm2835_probe(struct udevice *dev)
 
 	host->max_clk = bcm2835_get_mmc_clock(BCM2835_MBOX_CLOCK_ID_CORE);
 
+	bcm2835_set_sdhost_clock(0, &clock_rate[0], &clock_rate[1]);
+	host->firmware_sets_cdiv = (clock_rate[0] != ~0);
+
 	bcm2835_add_host(host);
 
 	dev_dbg(dev, "%s -> OK\n", __func__);