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

From: "Heiko Stübner" <heiko@sntech.de>
To: Shawn Lin <shawn.lin@rock-chips.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	linux-mmc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-rockchip@lists.infradead.org,
	Douglas Anderson <dianders@chromium.org>,
	Ziyuan Xu <xzy.xu@rock-chips.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] mmc: sdhci-of-arasan: Control clock for accessing syscon
Date: Mon, 29 Aug 2016 10:25:20 +0200	[thread overview]
Message-ID: <8418661.gal5ZOtGyv@diego> (raw)
In-Reply-To: <1472457779-7194-3-git-send-email-shawn.lin@rock-chips.com>

Hi Shawn,

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@rock-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.

Heiko