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

From: Shawn Lin
Date: Mon Aug 29 2016 - 05:21:09 EST

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@xxxxxxxxxxxxxx>
---

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