linux-kernel - Re: [PATCH v1 2/2] mmc: mediatek: add bus

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Date:   Sat, 29 Sep 2018 14:56:13 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Chaotian Jing <chaotian.jing@...iatek.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Sean Wang <sean.wang@...iatek.com>, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        srv_heupstream@...iatek.com
Subject: Re: [PATCH v1 2/2] mmc: mediatek: add bus_clk control



On 29/09/2018 04:29, 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@...iatek.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;

That means the bus_clk is not requiered, even for mt2712, although the binding
says so. Not sure if this is good enough or if we want to enforce the driver to
actually error out, when the clock is not present in a mt2712 DTS.

I suppose that's up to the maintainer :)

Regards,
Matthias