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

Shawn Lin
2016-08-29T09:20:46Z

On 2016/8/29 17:10, Heiko Stübner wrote:
> 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@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.
>>
>> 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.

except for other arasan's instances of some other venders who do have
soc-ctl-syscon but without any clk gate when accessing syscon,
possible? :)

>
>
>

--
Best Regards
Shawn Lin