On 11/1/23 16:33, Yang Xiwen wrote:
On 11/2/2023 2:50 AM, Yang Xiwen wrote:
On 11/2/2023 2:19 AM, Sean Anderson wrote:
On 8/17/23 13:04, Yang Xiwen via B4 Relay wrote:
From: Yang Xiwen <forbidden...@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.
OK, thank you for writing this up; it is clearer now. Please include this in
your commit message.
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.
Hm, what if we added something like clk_raw_enable, which just did
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 }
and the same thing for disable.
--Sean
