bcm2835-sdhost: Firmware manages the clock divisor

The bcm2835-sdhost driver hands control of the CDIV clock divisor
register to matching firmware, allowing it to adjust to a changing
core clock. This removes the need to use the performance governor or
to enable io_is_busy on the on-demand governor in order to get the
best SD performance.

N.B. As SD clocks must be an integer divisor of the core clock, it is
possible that the SD clock for "turbo" mode can be different (even
lower) than "normal" mode.

Signed-off-by: Phil Elwell <[email protected]>

Author: Phil Elwell

drivers/mmc/host/bcm2835-sdhost.c

@@ -50,6 +50,7 @@
 #include <linux/of_dma.h>
 #include <linux/time.h>
 #include <linux/workqueue.h>
+#include <soc/bcm2835/raspberrypi-firmware.h>
 
 #define DRIVER_NAME "sdhost-bcm2835"
 
@@ -190,6 +191,8 @@ struct bcm2835_host {
 	unsigned int			use_sbc:1;		/* Send CMD23 */
 
 	unsigned int			debug:1;		/* Enable debug output */
+	unsigned int			firmware_sets_cdiv:1;	/* Let the firmware manage the clock */
+	unsigned int			reset_clock:1;		/* Reset the clock fore the next request */
 
 	/*DMA part*/
 	struct dma_chan			*dma_chan_rxtx;		/* DMA channel for reads and writes */
@@ -437,7 +440,7 @@ static void bcm2835_sdhost_reset_internal(struct bcm2835_host *host)
 	host->clock = 0;
 	host->sectors = 0;
 	bcm2835_sdhost_write(host, host->hcfg, SDHCFG);
-	bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
+	bcm2835_sdhost_write(host, SDCDIV_MAX_CDIV, SDCDIV);
 	mmiowb();
 }
 
@@ -1510,6 +1513,7 @@ void bcm2835_sdhost_set_clock(struct bcm2835_host *host, unsigned int clock)
 {
 	int div = 0; /* Initialized for compiler warning */
 	unsigned int input_clock = clock;
+	unsigned long flags;
 
 	if (host->debug)
 		pr_info("%s: set_clock(%d)\n", mmc_hostname(host->mmc), clock);
@@ -1541,62 +1545,84 @@ void bcm2835_sdhost_set_clock(struct bcm2835_host *host, unsigned int clock)
 
 	host->mmc->actual_clock = 0;
 
-	if (clock < 100000) {
-	    /* Can't stop the clock, but make it as slow as possible
-	     * to show willing
-	     */
-	    host->cdiv = SDCDIV_MAX_CDIV;
-	    bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
-	    return;
-	}
+	if (host->firmware_sets_cdiv) {
+		u32 msg[3] = { clock, 0, 0 };
 
-	div = host->max_clk / clock;
-	if (div < 2)
-		div = 2;
-	if ((host->max_clk / div) > clock)
-		div++;
-	div -= 2;
+		rpi_firmware_property(rpi_firmware_get(NULL),
+				      RPI_FIRMWARE_SET_SDHOST_CLOCK,
+				      &msg, sizeof(msg));
 
-	if (div > SDCDIV_MAX_CDIV)
-	    div = SDCDIV_MAX_CDIV;
+		clock = max(msg[1], msg[2]);
+		spin_lock_irqsave(&host->lock, flags);
+	} else {
+		spin_lock_irqsave(&host->lock, flags);
+		if (clock < 100000) {
+			/* Can't stop the clock, but make it as slow as
+			 * possible to show willing
+			 */
+			host->cdiv = SDCDIV_MAX_CDIV;
+			bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
+			mmiowb();
+			spin_unlock_irqrestore(&host->lock, flags);
+			return;
+		}
 
-	clock = host->max_clk / (div + 2);
-	host->mmc->actual_clock = clock;
+		div = host->max_clk / clock;
+		if (div < 2)
+			div = 2;
+		if ((host->max_clk / div) > clock)
+			div++;
+		div -= 2;
+
+		if (div > SDCDIV_MAX_CDIV)
+			div = SDCDIV_MAX_CDIV;
+
+		clock = host->max_clk / (div + 2);
+
+		host->cdiv = div;
+		bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
+
+		if (host->debug)
+			pr_info("%s: clock=%d -> max_clk=%d, cdiv=%x "
+				"(actual clock %d)\n",
+				mmc_hostname(host->mmc), input_clock,
+				host->max_clk, host->cdiv,
+				clock);
+	}
 
 	/* Calibrate some delays */
 
 	host->ns_per_fifo_word = (1000000000/clock) *
 		((host->mmc->caps & MMC_CAP_4_BIT_DATA) ? 8 : 32);
 
-	if (clock > input_clock) {
-		/* Save the closest value, to make it easier
-		   to reduce in the event of error */
-		host->overclock_50 = (clock/MHZ);
+	if (input_clock == 50 * MHZ) {
+		if (clock > input_clock) {
+			/* Save the closest value, to make it easier
+			   to reduce in the event of error */
+			host->overclock_50 = (clock/MHZ);
 
-		if (clock != host->overclock) {
-			pr_warn("%s: overclocking to %dHz\n",
-				mmc_hostname(host->mmc), clock);
-			host->overclock = clock;
+			if (clock != host->overclock) {
+				pr_warn("%s: overclocking to %dHz\n",
+					mmc_hostname(host->mmc), clock);
+				host->overclock = clock;
+			}
+		} else if (host->overclock) {
+			host->overclock = 0;
+			if (clock == 50 * MHZ)
+				pr_warn("%s: cancelling overclock\n",
+					mmc_hostname(host->mmc));
 		}
 	}
-	else if (host->overclock)
-	{
-		host->overclock = 0;
-		if (clock == 50 * MHZ)
-			pr_warn("%s: cancelling overclock\n",
-				mmc_hostname(host->mmc));
-	}
-
-	host->cdiv = div;
-	bcm2835_sdhost_write(host, host->cdiv, SDCDIV);
 
 	/* Set the timeout to 500ms */
-	bcm2835_sdhost_write(host, host->mmc->actual_clock/2, SDTOUT);
+	bcm2835_sdhost_write(host, clock/2, SDTOUT);
 
-	if (host->debug)
-		pr_info("%s: clock=%d -> max_clk=%d, cdiv=%x (actual clock %d)\n",
-			mmc_hostname(host->mmc), input_clock,
-			host->max_clk, host->cdiv, host->mmc->actual_clock);
+	host->mmc->actual_clock = clock;
+	host->clock = input_clock;
+	host->reset_clock = 0;
+
+	mmiowb();
+	spin_unlock_irqrestore(&host->lock, flags);
 }
 
 static void bcm2835_sdhost_request(struct mmc_host *mmc, struct mmc_request *mrq)
@@ -1645,6 +1671,9 @@ static void bcm2835_sdhost_request(struct mmc_host *mmc, struct mmc_request *mrq
 	    (mrq->data->blocks > host->pio_limit))
 		bcm2835_sdhost_prepare_dma(host, mrq->data);
 
+	if (host->reset_clock)
+	    bcm2835_sdhost_set_clock(host, host->clock);
+
 	spin_lock_irqsave(&host->lock, flags);
 
 	WARN_ON(host->mrq != NULL);
@@ -1711,11 +1740,6 @@ static void bcm2835_sdhost_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 
 	log_event("IOS<", ios->clock, 0);
 
-	if (!ios->clock || ios->clock != host->clock) {
-		bcm2835_sdhost_set_clock(host, ios->clock);
-		host->clock = ios->clock;
-	}
-
 	/* set bus width */
 	host->hcfg &= ~SDHCFG_WIDE_EXT_BUS;
 	if (ios->bus_width == MMC_BUS_WIDTH_4)
@@ -1731,6 +1755,9 @@ static void bcm2835_sdhost_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 	mmiowb();
 
 	spin_unlock_irqrestore(&host->lock, flags);
+
+	if (!ios->clock || ios->clock != host->clock)
+		bcm2835_sdhost_set_clock(host, ios->clock);
 }
 
 static struct mmc_host_ops bcm2835_sdhost_ops = {
@@ -1802,7 +1829,7 @@ static void bcm2835_sdhost_tasklet_finish(unsigned long param)
 			host->overclock_50--;
 			pr_warn("%s: reducing overclock due to errors\n",
 				mmc_hostname(host->mmc));
-			bcm2835_sdhost_set_clock(host,50*MHZ);
+			host->reset_clock = 1;
 			mrq->cmd->error = -EILSEQ;
 			mrq->cmd->retries = 1;
 		}
@@ -1959,6 +1986,7 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
 	struct resource *iomem;
 	struct bcm2835_host *host;
 	struct mmc_host *mmc;
+	u32 msg[3];
 	int ret;
 
 	pr_debug("bcm2835_sdhost_probe\n");
@@ -1970,7 +1998,6 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
 	mmc->ops = &bcm2835_sdhost_ops;
 	host = mmc_priv(mmc);
 	host->mmc = mmc;
-	host->cmd_quick_poll_retries = 0;
 	host->pio_timeout = msecs_to_jiffies(500);
 	host->pio_limit = 1;
 	host->max_delay = 1; /* Warn if over 1ms */
@@ -2059,6 +2086,16 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)
 	else
 		mmc->caps |= MMC_CAP_4_BIT_DATA;
 
+	msg[0] = 0;
+	msg[1] = ~0;
+	msg[2] = ~0;
+
+	rpi_firmware_property(rpi_firmware_get(NULL),
+			      RPI_FIRMWARE_SET_SDHOST_CLOCK,
+			      &msg, sizeof(msg));
+
+	host->firmware_sets_cdiv = (msg[1] != ~0);
+
 	ret = bcm2835_sdhost_add_host(host);
 	if (ret)
 		goto err;

include/soc/bcm2835/raspberrypi-firmware.h

@@ -76,6 +76,7 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_SET_VOLTAGE =                            0x00038003,
 	RPI_FIRMWARE_SET_TURBO =                              0x00038009,
 	RPI_FIRMWARE_SET_CUSTOMER_OTP =                       0x00038021,
+	RPI_FIRMWARE_SET_SDHOST_CLOCK =                       0x00038042,
 
 	/* Dispmanx TAGS */
 	RPI_FIRMWARE_FRAMEBUFFER_ALLOCATE =                   0x00040001,