Re: [PATCH v1 9/9] coresight: Consolidate clock enabling

On Tue, Apr 01, 2025 at 03:58:42PM +0100, James Clark wrote:

[...]

...

/*

• • Attempt to find and enable "APB clock" for the given device

• • Attempt to find and enable programming clock (pclk) and trace clock (atclk)
• • for the given device.

• • Returns:

• • The AMBA bus driver will cover the pclk, to avoid duplicate operations,
• • skip to get and enable the pclk for an AMBA device.

• • clk - Clock is found and enabled
• • NULL - Clock is not needed as it is managed by the AMBA bus driver
• • ERROR - Clock is found but failed to enable

• • atclk is an optional clock, it will be only enabled when it is existed.
• • Otherwise, a NULL pointer will be returned to caller.
• • Returns: '0' on Success; Error code otherwise.
  */

-static inline struct clk *coresight_get_enable_apb_pclk(struct device *dev) +static inline int coresight_get_enable_clocks(struct device *dev,

• 			      struct clk **pclk,
  

• 			      struct clk **atclk)
  

This function has grown a bit now, probably best to remove it from the header and export it instead.

Sure. I can move this function into coresight-core.c file.

...

{

• struct clk *pclk = NULL;

• WARN_ON(!pclk); if (!dev_is_amba(dev)) {

• pclk = devm_clk_get_enabled(dev, "apb_pclk");
  

• if (IS_ERR(pclk))
  

• 	pclk = devm_clk_get_enabled(dev, "apb");
  

• *pclk = devm_clk_get_enabled(dev, "apb_pclk");
  

• if (IS_ERR(*pclk))
  

• 	*pclk = devm_clk_get_enabled(dev, "apb");
  

• if (IS_ERR(*pclk))
  

• 	return PTR_ERR(*pclk);
  

• } else {

• /* Don't enable pclk for an AMBA device */
  

• *pclk = NULL;
  

Now the "apb" clock won't be enabled for amba devices. I'm assuming that's fine if the clock was always called "apb_pclk" for them, but the commit that added the new clock name didn't specify any special casing either.

Can we have a comment that says it's deliberate? But the more I think about it the more I'm confused why CTCU needed a different clock name to be defined, when all the other Coresight devices use "apb_pclk".

Yes, seems to me, "apb" clock is the same thing with "apb_pclk". As CTCU DT binding has been merged, for backward compatible, we cannot remove it now.

CTCU driver only supports static probe, it is never probed by AMBA bus driver. I think this is another reason that "apb_pclk" is not used in CTCU driver. I can add a comment like:

"apb_pclk" is the default clock name used by the AMBA bus driver, while "apb" is used only by the CTCU driver. A CoreSight driver should use "apb_pclk" as its programming clock name.

Thanks, Leo

...

}

• return pclk;

• if (atclk) {

• *atclk = devm_clk_get_optional_enabled(dev, "atclk");
  

• if (IS_ERR(*atclk))
  

• 	return PTR_ERR(*atclk);
  

• }
• return 0; } #define CORESIGHT_PIDRn(i) (0xFE0 + ((i) * 4))