linux-kernel - Re: [PATCH 2/4] mmc: sdhci-of-arasan: Control clock for accessing syscon

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Date:   Mon, 29 Aug 2016 11:10:05 +0200
From:   Heiko Stübner <heiko@...ech.de>
To:     Shawn Lin <shawn.lin@...k-chips.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Douglas Anderson <dianders@...omium.org>,
        Ziyuan Xu <xzy.xu@...k-chips.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mmc: sdhci-of-arasan: Control clock for accessing syscon

Hi Shawn,

Am Montag, 29. August 2016, 16:54:10 schrieb Shawn Lin:
> On 2016/8/29 16:25, Heiko Stübner wrote:
> > Am Montag, 29. August 2016, 16:02:57 schrieb Shawn Lin:
> >> In the eariler commit 65820199272d ("Documentation: mmc:
> >> sdhci-of-arasan: Add soc-ctl-syscon for corecfg regs"), we
> >> introduced syscon to control corecfg_* stuff provided by
> >> arasan. But given that we may need to ungate the clock for
> >> accessing corecfg_*, it not so perfect as it depends on
> >> whether specific clock driver disables it if not referenced.
> >> Meanwhile, if we don't need arasan contoller to work anymore,
> >> there is no reason to still enable it. So let's control this
> >> clock when needed.
> >> 
> >> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
> >> ---
> >> 
> >>  drivers/mmc/host/sdhci-of-arasan.c | 25 ++++++++++++++++++++++---
> >>  1 file changed, 22 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/drivers/mmc/host/sdhci-of-arasan.c
> >> b/drivers/mmc/host/sdhci-of-arasan.c index 0b3a9cf..7ae3ae4 100644
> >> --- a/drivers/mmc/host/sdhci-of-arasan.c
> >> +++ b/drivers/mmc/host/sdhci-of-arasan.c
> >> @@ -78,6 +78,7 @@ struct sdhci_arasan_soc_ctl_map {
> >> 
> >>   * struct sdhci_arasan_data
> >>   * @host:		Pointer to the main SDHCI host structure.
> >>   * @clk_ahb:		Pointer to the AHB clock
> >> 
> >> + * @clk_syscon:		Pointer to the optional clock for accessing syscon
> >> 
> >>   * @phy:		Pointer to the generic phy
> >>   * @is_phy_on:		True if the PHY is on; false if not.
> >>   * @sdcardclk_hw:	Struct for the clock we might provide to a PHY.
> >> 
> >> @@ -88,6 +89,7 @@ struct sdhci_arasan_soc_ctl_map {
> >> 
> >>  struct sdhci_arasan_data {
> >>  
> >>  	struct sdhci_host *host;
> >>  	struct clk	*clk_ahb;
> >> 
> >> +	struct clk	*clk_syscon;
> >> 
> >>  	struct phy	*phy;
> >>  	bool		is_phy_on;
> >> 
> >> @@ -290,6 +292,7 @@ static int sdhci_arasan_suspend(struct device *dev)
> >> 
> >>  	clk_disable(pltfm_host->clk);
> >>  	clk_disable(sdhci_arasan->clk_ahb);
> >> 
> >> +	clk_disable(sdhci_arasan->clk_syscon);
> >> 
> >>  	return 0;
> >>  
> >>  }
> >> 
> >> @@ -309,6 +312,12 @@ static int sdhci_arasan_resume(struct device *dev)
> >> 
> >>  	struct sdhci_arasan_data *sdhci_arasan = sdhci_pltfm_priv(pltfm_host);
> >>  	int ret;
> >> 
> >> +	ret = clk_enable(sdhci_arasan->clk_syscon);
> >> +	if (ret) {
> >> +		dev_err(dev, "Cannot enable syscon clock.\n");
> >> +		return ret;
> >> +	}
> >> +
> >> 
> >>  	ret = clk_enable(sdhci_arasan->clk_ahb);
> >>  	if (ret) {
> >>  	
> >>  		dev_err(dev, "Cannot enable AHB clock.\n");
> >> 
> >> @@ -528,26 +537,33 @@ static int sdhci_arasan_probe(struct
> >> platform_device
> >> *pdev) ret);
> >> 
> >>  			goto err_pltfm_free;
> >>  		
> >>  		}
> >> 
> >> +
> >> +		sdhci_arasan->clk_syscon = devm_clk_get(&pdev->dev,
> >> +							"clk_syscon");
> >> +		if (clk_prepare_enable(sdhci_arasan->clk_syscon)) {
> >> +			dev_err(&pdev->dev, "Unable to enable syscon clock.\n");
> >> +			goto err_pltfm_free;
> >> +		}
> > 
> > doesn't look very "optional" to me.
> > clk_get specifies:
> > "Returns a struct clk corresponding to the clock producer, or
> > valid IS_ERR() condition containing errno."
> > 
> > So later clk_* on that err_ptr will produce failures and the
> > clock-framework could also request deferal.
> 
> Thanks for quick feedback.:)
> 
> It makes sense. I think it's just because clk_get request deferral, so
> we could simply assign NULL to cly_syscon and let clk_* return 0
> directly. So the deferral should be handle when getting other clks like
> clk_ahb?

nope, I think the position itself is fine, so just do something like

if (IS_ERR(sdhci_arasan->clk_syscon)) {
{
	if (PTR_ERR(sdhci_arasan->clk_syscon) == -EPROBE_DEFER)
		return -EPROBE_DEFER;
	else
		sdhci_arasan->clk_syscon = NULL;
}

as the syscon clk would only ever be necessary if the soc-ctl-syscon is 
actually defined. But there is no need to move that section I think.