Richard Zhao richard.zhao@freescale.com writes:
On Wed, Jan 11, 2012 at 03:22:34PM -0800, Kevin Hilman wrote:
Richard Zhao richard.zhao@linaro.org writes:
The driver get cpu operation point table from device tree cpu0 node,
Since we already have an existing OPP infrastructure in the kernel, seems like this driver should get OPPs by asking the OPP layer.
When I created the patch, there's only omap cpufreq driver using OPP. If it depends on OPP, it might prevent users who have not adopted OPP from using the driver.
Then they should probably adopt to OPP, since it was created exactly for this purpose. What this patch creates is an alternate way of adding OPPs using the device tree.
The point is using a static list of OPPs from boot time simply doesn't work. You need the ability to dynamically add/remove OPPs at runtime to adjust for various operating conditons (or HW bugs) as well as for thermal considerations. The OPP layer provides this.
A generic driver should get available OPPs using the OPP layer.
The DT can certainly be used at boot time to create the initial list of OPPs, but as the list of available OPPs changes at runtime, the only way to track that is to use the OPP layer.
This approach assumes the OPP layer is static at boot time and not changing, however that's not the case in practice.
The OPP layer could be extended to read boot-time OPPs from DT if desired, but since the OPPs are also populated/enabled/disabled dynamicaly on some platforms (e.g. OMAP), I think the any generic CPUfreq driver should use the OPP interface and not DT directly.
and adjusts operating points using clk and regulator APIs.
For a generic driver, the regulator used should also be configurable.
For example, this driver currently assumes a regulator named "cpu" for all instances. If you had separate clusters with independent voltage control, you'd likely have a separate regulator for each cluster.
The driver, for now, assumes all cpu cores uses the same clk and voltage. It's correct for most arm multi-core SoC.
Sure, but a "generic" driver such as the one proposed is not just for ARM, and not just for today's SoCs. flexible enough
Do you have real case to need different voltage/clk?
Sure, any system with independently scalable CPUs/clusters.
Kevin