Re: [alsa-devel] [PATCH v5 1/6] ASoC: Intel: Skylake: Add ssp clock driver

["Subhransu S. Prusty" <subhransu.s.prusty@intel.com>]

On Mon, Dec 18, 2017 at 11:10:40AM -0800, Stephen Boyd wrote:
> On 12/18, Subhransu S. Prusty wrote:
> > On Mon, Dec 18, 2017 at 09:27:16AM +0530, Subhransu S. Prusty wrote:
> > > On Wed, Dec 13, 2017 at 02:30:32PM -0800, Stephen Boyd wrote:
> > > > On 12/11, Sriram Periyasamy wrote:
> > > > 
> > > > > +
> > > > > +	if (!rate)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	if (__clk_is_enabled(hw->clk) && (clkdev->rate != rate))
> > > > 
> > > > Any chance you can directly read the hardware instead of going
> > > > through the framework to find out if the clk is enabled? Seems
> > > 
> > > No. This involves sending an IPC to DSP to enable clock and interpreting the
> > > return error code. I would like to avoid doing this here in set_rate.
> > > 
> 
> Ok. So we're checking to see if software has already enabled the
> clk and then checking to see if the rate the consumer is
> requesting is the same as the rate it previously requested? I'm

The second check is not required, will remove it.

> still confused what's going on here. Does skl_fill_clk_ipc()
> change the rate of the clk? Is there any way to ask the DSP what

skl_fill_clk_ipc() prepares the IPC message based on the rate request by the
consumer. This IPC will be sent to DSP during a call to clock enable.

> the rate would be if we were to use some rate configuration?

No. If the clock is already running, reconfiguration is not allowed. So the
above check is invalid.

> 
> > > > circular to do it this way.
> > > > 
> > > > > +		return -EBUSY;
> > > > > +
> > > > > +	rcfg = skl_get_rate_cfg(clkdev->pdata->ssp_clks[clkdev->id].rate_cfg,
> > > > > +							rate);
> > > > > +	if (!rcfg)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	clk_type = skl_get_clk_type(clkdev->id);
> > > > > +	if (clk_type < 0)
> > > > > +		return clk_type;
> > > > > +
> > > > > +	skl_fill_clk_ipc(rcfg, clk_type);
> > > > > +	clkdev->rate = rate;
> > > > > +
> > > > > +	return 0;
> > > > > +}
> > > > > +
> > > > > +static unsigned long skl_clk_recalc_rate(struct clk_hw *hw,
> > > > > +				unsigned long parent_rate)
> > > > > +{
> > > > > +	struct skl_clk *clkdev = to_skl_clk(hw);
> > > > > +	struct skl_clk_rate_cfg_table *rcfg;
> > > > > +	int clk_type;
> > > > > +
> > > > > +	if (!clkdev)
> > > > > +		return 0;
> > > > > +
> > > > > +	if (clkdev->rate)
> > > > > +		return clkdev->rate;
> > > > 
> > > > Why is the rate being cached? We should always be able to
> > > > calculate the rate based on parent_rate that gets passed to this
> > > > function?
> > > 
> > > Will check and get back.
> > 
> > If I understand correctly, you refer to deriving the rate from parent_rate
> > using ratios. But since only the DSP is aware of the ratios and not the
> > driver, the driver can't derive the rate from the parent_rate and thus
> > cached.
> > 
> 
> I was thinking the code would do what's below all the time.

I think we interpreted incorrectly. As recalc_rate is meant to be used only
when parent_rate changes, so this can be removed as the set_parent is not
supported for this driver. Please let me know if I understand correctly.


Regards,
Subhransu

> 
> > > 
> > > > 
> > > > > +
> > > > > +	rcfg = skl_get_rate_cfg(clkdev->pdata->ssp_clks[clkdev->id].rate_cfg,
> > > > > +					parent_rate);
> > > > > +	if (!rcfg)
> > > > > +		return 0;
> > > > > +
> > > > > +	clk_type = skl_get_clk_type(clkdev->id);
> > > > > +	if (clk_type < 0)
> > > > > +		return 0;
> > > > > +
> > > > > +	skl_fill_clk_ipc(rcfg, clk_type);
> > > > > +	clkdev->rate = rcfg->rate;
> > > > > +
> > > > > +	return clkdev->rate;
> > > > > +}
> > > > > +
> 
> I guess that means doing an IPC to the DSP to figure out the
> ratio and how that relates to the parent rate? recalc_rate() can
> be called many times with different things when the framework is
> speculating on the tree. We don't want clk providers to rely on
> the order of this op being called with respect to clk_set_rate().
> 
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project

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