mmc: sdhci-of-aspeed: Allow max-frequency limitation of SDCLK

Add a get_max_clock() handler to sdhci-of-aspeed to report f_max as the
maximum clock rate if it is set. This enables artificial limitation of
the bus speed via max-frequency in the devicetree for e.g. the AST2600
evaluation board where I was seeing errors at 200MHz.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci-of-aspeed.c

@@ -52,16 +52,24 @@ static void aspeed_sdc_configure_8bit_mode(struct aspeed_sdc *sdc,
 
 static void aspeed_sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 {
+	struct sdhci_pltfm_host *pltfm_host;
+	unsigned long parent;
 	int div;
 	u16 clk;
 
+	pltfm_host = sdhci_priv(host);
+	parent = clk_get_rate(pltfm_host->clk);
+
 	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
 
 	if (clock == 0)
 		return;
 
+	if (WARN_ON(clock > host->max_clk))
+		clock = host->max_clk;
+
 	for (div = 1; div < 256; div *= 2) {
-		if ((host->max_clk / div) <= clock)
+		if ((parent / div) <= clock)
 			break;
 	}
 	div >>= 1;
@@ -71,6 +79,14 @@ static void aspeed_sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 	sdhci_enable_clk(host, clk);
 }
 
+static unsigned int aspeed_sdhci_get_max_clock(struct sdhci_host *host)
+{
+	if (host->mmc->f_max)
+		return host->mmc->f_max;
+
+	return sdhci_pltfm_clk_get_max_clock(host);
+}
+
 static void aspeed_sdhci_set_bus_width(struct sdhci_host *host, int width)
 {
 	struct sdhci_pltfm_host *pltfm_priv;
@@ -97,7 +113,7 @@ static void aspeed_sdhci_set_bus_width(struct sdhci_host *host, int width)
 
 static const struct sdhci_ops aspeed_sdhci_ops = {
 	.set_clock = aspeed_sdhci_set_clock,
-	.get_max_clock = sdhci_pltfm_clk_get_max_clock,
+	.get_max_clock = aspeed_sdhci_get_max_clock,
 	.set_bus_width = aspeed_sdhci_set_bus_width,
 	.get_timeout_clock = sdhci_pltfm_clk_get_max_clock,
 	.reset = sdhci_reset,