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

Heiko Stübner
2016-08-29T10:46:14Z

Am Montag, 29. August 2016, 17:22:27 schrieb Shawn Lin:
> 在 2016/8/29 17:10, Heiko Stübner 写道:
> > 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 some arasan's instances for some other vendors who do have
> soc-ctl-syscon to control corecfg_* but without any clk gate for the
> accessing path, is it possible? :)

sure, if your struct clk reference is NULL, all the clk_* functions will just
return sucessful ... see [0] and friends. So essentially you just handle the
EPROBE_DEFER, because that means the clock is specified in the dts but not
available yet and just ignore other errors by setting the clk to NULL.

[0] http://lxr.free-electrons.com/source/drivers/clk/clk.c#L774