[PATCH 2/2] mmc: mediatek: add bus_clk control

[sean.wang@mediatek.com (Sean Wang)]

Hi,

On Fri, 2018-09-28 at 19:40 +0800, Chaotian Jing wrote:
> when gate MSDC0_HCLK, access register will hang, even the MSDC driver
> will never accessing register after HCLK was gated, but for safety, need
> gate the bus_clk(which used to access register) too.
> 
> Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
> ---
>  drivers/mmc/host/mtk-sd.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c
> index 0484138..1c1c967 100644
> --- a/drivers/mmc/host/mtk-sd.c
> +++ b/drivers/mmc/host/mtk-sd.c
> @@ -387,6 +387,7 @@ struct msdc_host {
>  
>  	struct clk *src_clk;	/* msdc source clock */
>  	struct clk *h_clk;      /* msdc h_clk */
> +	struct clk *bus_clk;	/* bus clock which used to access register */
>  	struct clk *src_clk_cg; /* msdc source clock control gate */
>  	u32 mclk;		/* mmc subsystem clock frequency */
>  	u32 src_clk_freq;	/* source clock frequency */
> @@ -660,12 +661,14 @@ 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->bus_clk);
>  	clk_disable_unprepare(host->h_clk);
>  }
>  
>  static void msdc_ungate_clock(struct msdc_host *host)
>  {
>  	clk_prepare_enable(host->h_clk);
> +	clk_prepare_enable(host->bus_clk);
>  	clk_prepare_enable(host->src_clk);
>  	clk_prepare_enable(host->src_clk_cg);
>  	while (!(readl(host->base + MSDC_CFG) & MSDC_CFG_CKSTB))
> @@ -1900,6 +1903,9 @@ static int msdc_drv_probe(struct platform_device *pdev)
>  		goto host_free;
>  	}
>  
> +	host->bus_clk = devm_clk_get(&pdev->dev, "bus_clk");
> +	if (IS_ERR(host->bus_clk))
> +		host->bus_clk = NULL;

The implementation would cause all SoCs to treat the bus_clk as the optional.
It seems you should add a flag to see what SoC requires the bus_clk to successfully access the related registers.

>  	/*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))