mmc: mediatek: add support of source_cg clock

source clock need an independent cg to control, when doing clk mode
switch, need gate source clock to avoid hw issue(multi-bit sync hw hang)
Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
Tested-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mtk-sd.c

@@ -372,6 +372,7 @@ struct msdc_host {
 
 	struct clk *src_clk;	/* msdc source clock */
 	struct clk *h_clk;      /* msdc h_clk */
+	struct clk *src_clk_cg; /* msdc source clock control gate */
 	u32 mclk;		/* mmc subsystem clock frequency */
 	u32 src_clk_freq;	/* source clock frequency */
 	u32 sclk;		/* SD/MS bus clock frequency */
@@ -616,6 +617,7 @@ static void msdc_set_timeout(struct msdc_host *host, u32 ns, u32 clks)
 
 static void msdc_gate_clock(struct msdc_host *host)
 {
+	clk_disable_unprepare(host->src_clk_cg);
 	clk_disable_unprepare(host->src_clk);
 	clk_disable_unprepare(host->h_clk);
 }
@@ -624,6 +626,7 @@ static void msdc_ungate_clock(struct msdc_host *host)
 {
 	clk_prepare_enable(host->h_clk);
 	clk_prepare_enable(host->src_clk);
+	clk_prepare_enable(host->src_clk_cg);
 	while (!(readl(host->base + MSDC_CFG) & MSDC_CFG_CKSTB))
 		cpu_relax();
 }
@@ -692,6 +695,15 @@ static void msdc_set_mclk(struct msdc_host *host, unsigned char timing, u32 hz)
 			sclk = (host->src_clk_freq >> 2) / div;
 		}
 	}
+	sdr_clr_bits(host->base + MSDC_CFG, MSDC_CFG_CKPDN);
+	/*
+	 * As src_clk/HCLK use the same bit to gate/ungate,
+	 * So if want to only gate src_clk, need gate its parent(mux).
+	 */
+	if (host->src_clk_cg)
+		clk_disable_unprepare(host->src_clk_cg);
+	else
+		clk_disable_unprepare(clk_get_parent(host->src_clk));
 	if (host->dev_comp->clk_div_bits == 8)
 		sdr_set_field(host->base + MSDC_CFG,
 			      MSDC_CFG_CKMOD | MSDC_CFG_CKDIV,
@@ -700,10 +712,14 @@ static void msdc_set_mclk(struct msdc_host *host, unsigned char timing, u32 hz)
 		sdr_set_field(host->base + MSDC_CFG,
 			      MSDC_CFG_CKMOD_EXTRA | MSDC_CFG_CKDIV_EXTRA,
 			      (mode << 12) | div);
+	if (host->src_clk_cg)
+		clk_prepare_enable(host->src_clk_cg);
+	else
+		clk_prepare_enable(clk_get_parent(host->src_clk));
 
-	sdr_set_bits(host->base + MSDC_CFG, MSDC_CFG_CKPDN);
 	while (!(readl(host->base + MSDC_CFG) & MSDC_CFG_CKSTB))
 		cpu_relax();
+	sdr_set_bits(host->base + MSDC_CFG, MSDC_CFG_CKPDN);
 	host->sclk = sclk;
 	host->mclk = hz;
 	host->timing = timing;
@@ -1822,6 +1838,11 @@ static int msdc_drv_probe(struct platform_device *pdev)
 		goto host_free;
 	}
 
+	/*source clock control gate is optional clock*/
+	host->src_clk_cg = devm_clk_get(&pdev->dev, "source_cg");
+	if (IS_ERR(host->src_clk_cg))
+		host->src_clk_cg = NULL;
+
 	host->irq = platform_get_irq(pdev, 0);
 	if (host->irq < 0) {
 		ret = -EINVAL;