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

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Date:   Sat, 29 Sep 2018 10:39:42 +0800
From:   Chaotian Jing <chaotian.jing@...iatek.com>
To:     Sean Wang <sean.wang@...iatek.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.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 2/2] mmc: mediatek: add bus_clk control

On Sat, 2018-09-29 at 01:28 +0800, Sean Wang wrote:
> 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@...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;
> 
> 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.

>  Yes, but is no harm to other SoCs, just like the handle of "source_cg"
> >  	/*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))
> 
>