Messages in this thread | | | Subject | Re: [PATCH V5 11/18] clk: tegra210: Add support for Tegra210 clocks | From | Sowjanya Komatineni <> | Date | Tue, 16 Jul 2019 15:06:16 -0700 |
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On 7/16/19 3:00 PM, Dmitry Osipenko wrote: > 17.07.2019 0:35, Sowjanya Komatineni пишет: >> On 7/16/19 2:21 PM, Dmitry Osipenko wrote: >>> 17.07.2019 0:12, Sowjanya Komatineni пишет: >>>> On 7/16/19 1:47 PM, Dmitry Osipenko wrote: >>>>> 16.07.2019 22:26, Sowjanya Komatineni пишет: >>>>>> On 7/16/19 11:43 AM, Dmitry Osipenko wrote: >>>>>>> 16.07.2019 21:30, Sowjanya Komatineni пишет: >>>>>>>> On 7/16/19 11:25 AM, Dmitry Osipenko wrote: >>>>>>>>> 16.07.2019 21:19, Sowjanya Komatineni пишет: >>>>>>>>>> On 7/16/19 9:50 AM, Sowjanya Komatineni wrote: >>>>>>>>>>> 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... >>>>>>>>> Looks like I initially confused this case with getting orphaned >>>>>>>>> clock. >>>>>>>>> I'm now seeing that the DFLL driver registers the clock and then >>>>>>>>> clk_get(dfll) should be returning EPROBE_DEFER until DFLL driver is >>>>>>>>> probed, hence everything should be fine as-is and there is no real >>>>>>>>> need >>>>>>>>> for the 'device link'. Sorry for the confusion! >>>>>>>>> >>>>>>>>>>>>>> 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 >>>>>>>>>>> >>>>>>>>>> Sorry, please ignore my above comment. During suspend, need to >>>>>>>>>> change >>>>>>>>>> CCLK_G source to PLLP when dfll is in closed loop mode first and >>>>>>>>>> then >>>>>>>>>> dfll need to be set to open loop. >>>>>>>>> Okay. >>>>>>>>> >>>>>>>>>>>>>> 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 >>>>>>>>>>>>> >>>>>>>>>> I see during switch away from DFLL (suspend), cclk_g parent is not >>>>>>>>>> changed to PLLP before changing dfll to open loop mode. >>>>>>>>>> >>>>>>>>>> Will add this ... >>>>>>>>> The CPUFreq driver switches parent to PLLP during the probe, >>>>>>>>> similar >>>>>>>>> should be done on suspend. >>>>>>>>> >>>>>>>>> I'm also wondering if it's always safe to switch to PLLP in the >>>>>>>>> probe. >>>>>>>>> If CPU is running on a lower freq than PLLP, then some other more >>>>>>>>> appropriate intermediate parent should be selected. >>>>>>>>> >>>>>>>> CPU parents are PLL_X, PLL_P, and dfll. PLL_X always runs at higher >>>>>>>> rate >>>>>>>> so switching to PLL_P during CPUFreq probe prior to dfll clock >>>>>>>> enable >>>>>>>> should be safe. >>>>>>> AFAIK, PLLX could run at ~200MHz. There is also a divided output of >>>>>>> PLLP >>>>>>> which CCLKG supports, the PLLP_OUT4. >>>>>>> >>>>>>> Probably, realistically, CPU is always running off a fast PLLX during >>>>>>> boot, but I'm wondering what may happen on KEXEC. I guess ideally >>>>>>> CPUFreq driver should also have a 'shutdown' callback to teardown >>>>>>> DFLL >>>>>>> on a reboot, but likely that there are other clock-related >>>>>>> problems as >>>>>>> well that may break KEXEC and thus it is not very important at the >>>>>>> moment. >>>>>>> >>>>>>> [snip] >>>>>> During bootup CPUG sources from PLL_X. By PLL_P source above I meant >>>>>> PLL_P_OUT4. >>>>>> >>>>>> As per clock policies, PLL_X is always used for high freq like >800Mhz >>>>>> and for low frequency it will be sourced from PLLP. >>>>> Alright, then please don't forget to pre-initialize PLLP_OUT4 rate to a >>>>> reasonable value using tegra_clk_init_table or assigned-clocks. >>>> PLLP_OUT4 rate update is not needed as it is safe to run at 408Mhz >>>> because it is below fmax @ Vmin >>> So even 204MHz CVB entries are having the same voltage as 408MHz, >>> correct? It's not instantly obvious to me from the DFLL driver's code >>> where the fmax @ Vmin is defined, I see that there is the min_millivolts >>> and frequency entries starting from 204MHZ defined per-table. >> Yes at Vmin CPU Fmax is ~800Mhz. So anything below that will work at >> Vmin voltage and PLLP max is 408Mhz. > Thank you for the clarification. It would be good to have that commented > in the code as well. OK, Will add...
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