mmc: dw-mmc-rockchip: Fix handling invalid clock rates

The Rockchip rk356x ciu clock cannot be set as low as the dw-mmc
hardware supports. This leads to a situation during card initialization
where the clock is set lower than the clock driver can support. The
dw-mmc-rockchip driver spews errors when this happens.
For normal operation this only happens a few times during boot, but when
cd-broken is enabled (in cases such as the SoQuartz module) this fires
multiple times each poll cycle.

Fix this by testing the lowest possible frequency that the clock driver
can support which is within the mmc specification. Divide that rate by
the internal divider and set f_min to this.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Link: https://lore.kernel.org/r/20220305215835.2210388-3-pgwipeout@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc-rockchip.c

@@ -15,7 +15,9 @@
 #include "dw_mmc.h"
 #include "dw_mmc-pltfm.h"
 
-#define RK3288_CLKGEN_DIV       2
+#define RK3288_CLKGEN_DIV	2
+
+static const unsigned int freqs[] = { 100000, 200000, 300000, 400000 };
 
 struct dw_mci_rockchip_priv_data {
 	struct clk		*drv_clk;
@@ -51,7 +53,7 @@ static void dw_mci_rk3288_set_ios(struct dw_mci *host, struct mmc_ios *ios)
 
 	ret = clk_set_rate(host->ciu_clk, cclkin);
 	if (ret)
-		dev_warn(host->dev, "failed to set rate %uHz\n", ios->clock);
+		dev_warn(host->dev, "failed to set rate %uHz err: %d\n", cclkin, ret);
 
 	bus_hz = clk_get_rate(host->ciu_clk) / RK3288_CLKGEN_DIV;
 	if (bus_hz != host->bus_hz) {
@@ -290,13 +292,30 @@ static int dw_mci_rk3288_parse_dt(struct dw_mci *host)
 
 static int dw_mci_rockchip_init(struct dw_mci *host)
 {
+	int ret, i;
+
 	/* It is slot 8 on Rockchip SoCs */
 	host->sdio_id0 = 8;
 
-	if (of_device_is_compatible(host->dev->of_node,
-				    "rockchip,rk3288-dw-mshc"))
+	if (of_device_is_compatible(host->dev->of_node, "rockchip,rk3288-dw-mshc")) {
 		host->bus_hz /= RK3288_CLKGEN_DIV;
 
+		/* clock driver will fail if the clock is less than the lowest source clock
+		 * divided by the internal clock divider. Test for the lowest available
+		 * clock and set the minimum freq to clock / clock divider.
+		 */
+
+		for (i = 0; i < ARRAY_SIZE(freqs); i++) {
+			ret = clk_round_rate(host->ciu_clk, freqs[i] * RK3288_CLKGEN_DIV);
+			if (ret > 0) {
+				host->minimum_speed = ret / RK3288_CLKGEN_DIV;
+				break;
+			}
+		}
+		if (ret < 0)
+			dev_warn(host->dev, "no valid minimum freq: %d\n", ret);
+	}
+
 	return 0;
 }