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

Shawn Lin
2016-08-29T08:54:10Z

Hi Heiko,

On 2016/8/29 16:25, Heiko Stübner wrote:
> 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-TNX95d0MmH7DzftRWevZcw@public.gmane.org>
>> ---
>>
>> 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?

>
>
> Heiko
>
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--
Best Regards
Shawn Lin

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