mmc: tmio, sh_mobile_sdhi: Add support for variable input clock frequency

Currently tmio_mmc assumes that the input clock frequency is fixed and
only its own clock divider can be changed.  This is not true in the
case of sh_mobile_sdhi; we can use the clock API to change it.

In tmio_mmc:
- Delegate setting of f_min from tmio to the clk_enable operation (if
  implemented), as it can be smaller than f_max / 512
- Add an optional clk_update operation called from tmio_mmc_set_clock()
  that updates the input clock frequency
- Rename tmio_mmc_clk_update() to tmio_mmc_clk_enable(), to avoid
  confusion with the clk_update operation

In sh_mobile_sdhi:
- Make the setting of f_max conditional; it should be set through the
  max-frequency property in the device tree in future
- Set f_min based on the input clock's minimum frequency
- Implement the clk_update operation, selecting the best input clock
  frequency for the bus frequency that's wanted

sh_mobile_sdhi_clk_update() is loosely based on Kuninori Morimoto's work
in sh_mmcif.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sh_mobile_sdhi.c

@@ -139,7 +139,20 @@ static int sh_mobile_sdhi_clk_enable(struct tmio_mmc_host *host)
 	if (ret < 0)
 		return ret;
 
-	mmc->f_max = clk_get_rate(priv->clk);
+	/*
+	 * The clock driver may not know what maximum frequency
+	 * actually works, so it should be set with the max-frequency
+	 * property which will already have been read to f_max.  If it
+	 * was missing, assume the current frequency is the maximum.
+	 */
+	if (!mmc->f_max)
+		mmc->f_max = clk_get_rate(priv->clk);
+
+	/*
+	 * Minimum frequency is the minimum input clock frequency
+	 * divided by our maximum divider.
+	 */
+	mmc->f_min = max(clk_round_rate(priv->clk, 1) / 512, 1L);
 
 	/* enable 16bit data access on SDBUF as default */
 	sh_mobile_sdhi_sdbuf_width(host, 16);
@@ -147,6 +160,44 @@ static int sh_mobile_sdhi_clk_enable(struct tmio_mmc_host *host)
 	return 0;
 }
 
+static unsigned int sh_mobile_sdhi_clk_update(struct tmio_mmc_host *host,
+					      unsigned int new_clock)
+{
+	struct sh_mobile_sdhi *priv = host_to_priv(host);
+	unsigned int freq, best_freq, diff_min, diff;
+	int i;
+
+	diff_min = ~0;
+	best_freq = 0;
+
+	/*
+	 * We want the bus clock to be as close as possible to, but no
+	 * greater than, new_clock.  As we can divide by 1 << i for
+	 * any i in [0, 9] we want the input clock to be as close as
+	 * possible, but no greater than, new_clock << i.
+	 */
+	for (i = min(9, ilog2(UINT_MAX / new_clock)); i >= 0; i--) {
+		freq = clk_round_rate(priv->clk, new_clock << i);
+		if (freq > (new_clock << i)) {
+			/* Too fast; look for a slightly slower option */
+			freq = clk_round_rate(priv->clk,
+					      (new_clock << i) / 4 * 3);
+			if (freq > (new_clock << i))
+				continue;
+		}
+
+		diff = new_clock - (freq >> i);
+		if (diff <= diff_min) {
+			best_freq = freq;
+			diff_min = diff;
+		}
+	}
+
+	clk_set_rate(priv->clk, best_freq);
+
+	return best_freq;
+}
+
 static void sh_mobile_sdhi_clk_disable(struct tmio_mmc_host *host)
 {
 	struct sh_mobile_sdhi *priv = host_to_priv(host);
@@ -265,6 +316,7 @@ static int sh_mobile_sdhi_probe(struct platform_device *pdev)
 	host->dma		= dma_priv;
 	host->write16_hook	= sh_mobile_sdhi_write16_hook;
 	host->clk_enable	= sh_mobile_sdhi_clk_enable;
+	host->clk_update	= sh_mobile_sdhi_clk_update;
 	host->clk_disable	= sh_mobile_sdhi_clk_disable;
 	host->multi_io_quirk	= sh_mobile_sdhi_multi_io_quirk;
 
@@ -362,7 +414,7 @@ static int sh_mobile_sdhi_probe(struct platform_device *pdev)
 		}
 	}
 
-	dev_info(&pdev->dev, "%s base at 0x%08lx clock rate %u MHz\n",
+	dev_info(&pdev->dev, "%s base at 0x%08lx max clock rate %u MHz\n",
 		 mmc_hostname(host->mmc), (unsigned long)
 		 (platform_get_resource(pdev, IORESOURCE_MEM, 0)->start),
 		 host->mmc->f_max / 1000000);

drivers/mmc/host/tmio_mmc.h

@@ -96,6 +96,8 @@ struct tmio_mmc_host {
 
 	int (*write16_hook)(struct tmio_mmc_host *host, int addr);
 	int (*clk_enable)(struct tmio_mmc_host *host);
+	unsigned int (*clk_update)(struct tmio_mmc_host *host,
+				   unsigned int new_clock);
 	void (*clk_disable)(struct tmio_mmc_host *host);
 	int (*multi_io_quirk)(struct mmc_card *card,
 			      unsigned int direction, int blk_size);

drivers/mmc/host/tmio_mmc_pio.c

@@ -160,9 +160,12 @@ static void tmio_mmc_set_clock(struct tmio_mmc_host *host,
 	u32 clk = 0, clock;
 
 	if (new_clock) {
-		for (clock = host->mmc->f_min, clk = 0x80000080;
-		     new_clock >= (clock << 1);
-		     clk >>= 1)
+		if (host->clk_update)
+			clock = host->clk_update(host, new_clock) / 512;
+		else
+			clock = host->mmc->f_min;
+
+		for (clk = 0x80000080; new_clock >= (clock << 1); clk >>= 1)
 			clock <<= 1;
 
 		/* 1/1 clock is option */
@@ -837,19 +840,12 @@ fail:
 	pm_runtime_put_autosuspend(mmc_dev(mmc));
 }
 
-static int tmio_mmc_clk_update(struct tmio_mmc_host *host)
+static int tmio_mmc_clk_enable(struct tmio_mmc_host *host)
 {
-	struct mmc_host *mmc = host->mmc;
-	int ret;
-
 	if (!host->clk_enable)
 		return -ENOTSUPP;
 
-	ret = host->clk_enable(host);
-	if (!ret)
-		mmc->f_min = mmc->f_max / 512;
-
-	return ret;
+	return host->clk_enable(host);
 }
 
 static void tmio_mmc_power_on(struct tmio_mmc_host *host, unsigned short vdd)
@@ -1135,7 +1131,7 @@ int tmio_mmc_host_probe(struct tmio_mmc_host *_host,
 				  mmc->caps & MMC_CAP_NONREMOVABLE ||
 				  mmc->slot.cd_irq >= 0);
 
-	if (tmio_mmc_clk_update(_host) < 0) {
+	if (tmio_mmc_clk_enable(_host) < 0) {
 		mmc->f_max = pdata->hclk;
 		mmc->f_min = mmc->f_max / 512;
 	}
@@ -1263,7 +1259,7 @@ int tmio_mmc_host_runtime_resume(struct device *dev)
 	struct tmio_mmc_host *host = mmc_priv(mmc);
 
 	tmio_mmc_reset(host);
-	tmio_mmc_clk_update(host);
+	tmio_mmc_clk_enable(host);
 
 	if (host->clk_cache) {
 		tmio_mmc_set_clock(host, host->clk_cache);