On 7/16/19 8:00 AM, Dmitry Osipenko wrote:
16.07.2019 11:06, Peter De Schrijver пишет:
On Tue, Jul 16, 2019 at 03:24:26PM +0800, Joseph Lo wrote:
OK, Will add to CPUFreq driver...
The other thing that also need attention is that T124 CPUFreq driver
implicitly relies on DFLL driver to be probed first, which is icky.
Should I add check for successful dfll clk register explicitly in
CPUFreq driver probe and defer till dfll clk registers?
Probably you should use the "device links". See [1][2] for the example.
[1]
https://elixir.bootlin.com/linux/v5.2.1/source/drivers/gpu/drm/tegra/dc.c#L2383
[2] https://www.kernel.org/doc/html/latest/driver-api/device_link.html
Return EPROBE_DEFER instead of EINVAL if device_link_add() fails. And
use of_find_device_by_node() to get the DFLL's device, see [3].
[3]
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/devfreq/tegra20-devfreq.c#n100
Will go thru and add...
Sorry, I didn't follow the mail thread. Just regarding the DFLL part.
As you know it, the DFLL clock is one of the CPU clock sources and
integrated with DVFS control logic with the regulator. We will not switch
CPU to other clock sources once we switched to DFLL. Because the CPU has
been regulated by the DFLL HW with the DVFS table (CVB or OPP table you see
in the driver.). We shouldn't reparent it to other sources with unknew
freq/volt pair. That's not guaranteed to work. We allow switching to
open-loop mode but different sources.
Okay, then the CPUFreq driver will have to enforce DFLL freq to PLLP's
rate before switching to PLLP in order to have a proper CPU voltage.
PLLP freq is safe to work for any CPU voltage. So no need to enforce
DFLL freq to PLLP rate before changing CCLK_G source to PLLP during suspend
And I don't exactly understand why we need to switch to PLLP in CPU idle
driver. Just keep it on CL-DVFS mode all the time.
In SC7 entry, the dfll suspend function moves it the open-loop mode. That's
all. The sc7-entryfirmware will handle the rest of the sequence to turn off
the CPU power.
In SC7 resume, the warmboot code will handle the sequence to turn on
regulator and power up the CPU cluster. And leave it on PLL_P. After
resuming to the kernel, we re-init DFLL, restore the CPU clock policy (CPU
runs on DFLL open-loop mode) and then moving to close-loop mode.
The DFLL is re-inited after switching CCLK to DFLL parent during of the
early clocks-state restoring by CaR driver. Hence instead of having odd
hacks in the CaR driver, it is much nicer to have a proper
suspend-resume sequencing of the device drivers. In this case CPUFreq
driver is the driver that enables DFLL and switches CPU to that clock
source, which means that this driver is also should be responsible for
management of the DFLL's state during of suspend/resume process. If
CPUFreq driver disables DFLL during suspend and re-enables it during
resume, then looks like the CaR driver hacks around DFLL are not needed.
The DFLL part looks good to me. BTW, change the patch subject to "Add
suspend-resume support" seems more appropriate to me.
To clarify this, the sequences for DFLL use are as follows (assuming all
required DFLL hw configuration has been done)
Switch to DFLL:
0) Save current parent and frequency
1) Program DFLL to open loop mode
2) Enable DFLL
3) Change cclk_g parent to DFLL
For OVR regulator:
4) Change PWM output pin from tristate to output
5) Enable DFLL PWM output
For I2C regulator:
4) Enable DFLL I2C output
6) Program DFLL to closed loop mode
Switch away from DFLL:
0) Change cclk_g parent to PLLP so the CPU frequency is ok for any vdd_cpu voltage
1) Program DFLL to open loop mode
For OVR regulator:
2) Change PWM output pin from output to tristate: vdd_cpu will go back
to hardwired boot voltage.
3) Disable DFLL PWM output
For I2C regulator:
2) Program vdd_cpu regulator voltage to the boot voltage
3) Disable DFLL I2C output
4) Reprogram parent saved in step 0 of 'Switch to DFLL' to the saved
frequency
5) Change cclk_g parent to saved parent
6) Disable DFLL
This is the same sequence currently implemented. But dfll suspend/resume
calls are thru Tegra210 clock driver.
Dmitry wants to have dfll suspend/resume along with CCLK_G restore to
happen from CPUFreq driver pm_ops rather than tegra210 clock driver or
tegra dfll driver.
Will move it to CPUFreq driver...
Thanks!
