On 11/2/2023 2:50 AM, Yang Xiwen wrote:

On 11/2/2023 2:19 AM, Sean Anderson wrote:

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On 8/17/23 13:04, Yang Xiwen via B4 Relay wrote:

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From: Yang Xiwen forbidden405@outlook.com

Calling into CCF framework will cause a clock being enabled twice instead of once (clk->enable_count becomes 2 rather than 1), thus making it hard to disable (needs to call clk_disable() twice). Fix that by calling clock provided ops directly.

Can you describe this scenario more? From what I can tell, clk_enable doesn't increment enable_count for CCF clocks.

Well, it's hard to describe clearly. But I can only tell this patch fixed the issue when i was trying to write an Ethernet driver[1] which calls clk_disable() and expects the clock to be disabled after that. Also I found that CCF driver does not have a corresponding test file. I will try to write a test for that in next release.

Okay, fine. I read the source again and let me try to explain the whole thing to you briefly. Let's see what happens when we are calling clk_enable(gate).

The source of clk.c is listed below and labeled for clarity:

``` 1 if (CONFIG_IS_ENABLED(CLK_CCF)) { 2 /* Take id 0 as a non-valid clk, such as dummy */ 3 if (clk->id && !clk_get_by_id(clk->id, &clkp)) { 4 if (clkp->enable_count) { 5 clkp->enable_count++; 6 return 0; 7 } 8 if (clkp->dev->parent && 9 device_get_uclass_id(clkp->dev->parent) == UCLASS_CLK) { 10 ret = clk_enable(dev_get_clk_ptr(clkp->dev->parent)); 11 if (ret) { 12 printf("Enable %s failed\n", 13 clkp->dev->parent->name); 14 return ret; 15 } 16 } 17 } 18 19 if (ops->enable) { 20 ret = ops->enable(clk); 21 if (ret) { 22 printf("Enable %s failed\n", clk->dev->name); 23 return ret; 24 } 25 } 26 if (clkp) 27 clkp->enable_count++; 28 } else { 29 if (!ops->enable) 30 return -ENOSYS; 31 return ops->enable(clk); ```

The following steps are executed:

1. Actually, a "fake" clk is passed to clk_enable() and only clk->id is valid. The actual clk is "clkp"; 2. Initially, we runs till `ret = ops->enable(clk)`(line 20), i.e. ccf_clk_enable(clk); 3. Thankfully, ccf_clk_enable() calls clk_get_by_id() to get the real clk and call clk_enable(clkp) again so we won't have an endless loop here. 4. So ops->enable(clk) actually equals to clk_enable(clkp). It's obvious that there is a `clkp->enable_count++` inside the nested function call since it's still 0. Now it becomes 1; 5. The nested clk_enable(clkp) now returns to the outer clk_enable(clk); 6. Unfortunately, there is a `if (clkp) clkp->enable_count++;`(line 26) afterwards. Now it becomes 2. 7. Finally, we got a clk being enabled twice. "clkp->enable_count" is 2 now.

Obviously it's not the intended behavior. We can either fix clk_enable() or ccf_clk_endisable() to resolve this. But I choose to touch ccf_clk_endisable() since it's less commonly used.

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--Sean

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Signed-off-by: Yang Xiwen forbidden405@outlook.com

drivers/clk/clk.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index a38daaac0c..00d082c46f 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -14,6 +14,7 @@ #include <dm/uclass.h> #include <dm/lists.h> #include <dm/device-internal.h> +#include <linux/clk-provider.h> int clk_register(struct clk *clk, const char *drv_name, const char *name, const char *parent_name) @@ -115,11 +116,20 @@ int ccf_clk_set_parent(struct clk *clk, struct clk *parent) static int ccf_clk_endisable(struct clk *clk, bool enable) { struct clk *c;

• const struct clk_ops *ops; int err = clk_get_by_id(clk->id, &c); if (err) return err;

• return enable ? clk_enable(c) : clk_disable(c);

• else

•    ops = clk_dev_ops(c->dev);
  

• if (enable && ops->enable)

•    return ops->enable(c);
  

• else if (!enable && ops->disable)

•    return ops->disable(c);
  

• return -ENOSYS; } int ccf_clk_enable(struct clk *clk)

[1] https://lore.kernel.org/all/20230814-wip-hisi_femac-trunk-v2-0-1e29f400585d@...