[PATCH v3 2/3] mmc: sdhci-of-aspeed: Add AST2600 bus clock support

[Andrew Jeffery <andrew@aj.id.au>]

The AST2600 can achieve HS200 speeds with a change to the bus clock
divisor behaviour. The divisor can also be more accurate with respect
to the requested clock rate, but keep the one-hot behaviour for
backwards compatibility with the AST2400 and AST2500.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
---
 drivers/mmc/host/sdhci-of-aspeed.c | 37 ++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/mmc/host/sdhci-of-aspeed.c b/drivers/mmc/host/sdhci-of-aspeed.c
index 9fda2e7c1d78..52179b800e6c 100644
--- a/drivers/mmc/host/sdhci-of-aspeed.c
+++ b/drivers/mmc/host/sdhci-of-aspeed.c
@@ -65,6 +65,7 @@ struct aspeed_sdhci_phase_param {
 };
 
 struct aspeed_sdhci_pdata {
+	unsigned int clk_div_start;
 	const struct aspeed_sdhci_phase_desc *phase_desc;
 	size_t nr_phase_descs;
 };
@@ -207,10 +208,13 @@ static void aspeed_sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 {
 	struct sdhci_pltfm_host *pltfm_host;
 	unsigned long parent, bus;
+	struct aspeed_sdhci *sdhci;
 	int div;
 	u16 clk;
 
 	pltfm_host = sdhci_priv(host);
+	sdhci = sdhci_pltfm_priv(pltfm_host);
+
 	parent = clk_get_rate(pltfm_host->clk);
 
 	sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
@@ -221,7 +225,23 @@ static void aspeed_sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
 	if (WARN_ON(clock > host->max_clk))
 		clock = host->max_clk;
 
-	for (div = 2; div < 256; div *= 2) {
+	/*
+	 * Regarding the AST2600:
+	 *
+	 * If (EMMC12C[7:6], EMMC12C[15:8] == 0) then
+	 *   period of SDCLK = period of SDMCLK.
+	 *
+	 * If (EMMC12C[7:6], EMMC12C[15:8] != 0) then
+	 *   period of SDCLK = period of SDMCLK * 2 * (EMMC12C[7:6], EMMC[15:8])
+	 *
+	 * If you keep EMMC12C[7:6] = 0 and EMMC12C[15:8] as one-hot,
+	 * 0x1/0x2/0x4/etc, you will find it is compatible to AST2400 or AST2500
+	 *
+	 * Keep the one-hot behaviour for backwards compatibility except for
+	 * supporting the value 0 in (EMMC12C[7:6], EMMC12C[15:8]), and capture
+	 * the 0-value capability in clk_div_start.
+	 */
+	for (div = sdhci->pdata->clk_div_start; div < 256; div *= 2) {
 		bus = parent / div;
 		if (bus <= clock)
 			break;
@@ -374,6 +394,10 @@ static int aspeed_sdhci_probe(struct platform_device *pdev)
 	int ret;
 
 	aspeed_pdata = of_device_get_match_data(&pdev->dev);
+	if (!aspeed_pdata) {
+		dev_err(&pdev->dev, "Missing platform configuration data\n");
+		return -EINVAL;
+	}
 
 	host = sdhci_pltfm_init(pdev, &aspeed_sdhci_pdata, sizeof(*dev));
 	if (IS_ERR(host))
@@ -392,7 +416,7 @@ static int aspeed_sdhci_probe(struct platform_device *pdev)
 	else if (slot >= 2)
 		return -EINVAL;
 
-	if (dev->pdata && slot < dev->pdata->nr_phase_descs) {
+	if (slot < dev->pdata->nr_phase_descs) {
 		dev->phase_desc = &dev->pdata->phase_desc[slot];
 	} else {
 		dev_info(&pdev->dev,
@@ -455,6 +479,10 @@ static int aspeed_sdhci_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static const struct aspeed_sdhci_pdata ast2400_sdhci_pdata = {
+	.clk_div_start = 2,
+};
+
 static const struct aspeed_sdhci_phase_desc ast2600_sdhci_phase[] = {
 	/* SDHCI/Slot 0 */
 	[0] = {
@@ -485,13 +513,14 @@ static const struct aspeed_sdhci_phase_desc ast2600_sdhci_phase[] = {
 };
 
 static const struct aspeed_sdhci_pdata ast2600_sdhci_pdata = {
+	.clk_div_start = 1,
 	.phase_desc = ast2600_sdhci_phase,
 	.nr_phase_descs = ARRAY_SIZE(ast2600_sdhci_phase),
 };
 
 static const struct of_device_id aspeed_sdhci_of_match[] = {
-	{ .compatible = "aspeed,ast2400-sdhci", },
-	{ .compatible = "aspeed,ast2500-sdhci", },
+	{ .compatible = "aspeed,ast2400-sdhci", .data = &ast2400_sdhci_pdata, },
+	{ .compatible = "aspeed,ast2500-sdhci", .data = &ast2400_sdhci_pdata, },
 	{ .compatible = "aspeed,ast2600-sdhci", .data = &ast2600_sdhci_pdata, },
 	{ }
 };
-- 
2.27.0