| Message ID | 20240610120025.405062-1-gnstark@salutedevices.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | pwm-regulator with voltage table problem | expand |
On Mon, Jun 10, 2024 at 03:00:24PM +0300, George Stark wrote:
> Here is the situation we've met on an ARM SoC:
Please don't send cover letters for single patches, if there is anything
that needs saying put it in the changelog of the patch or after the ---
if it's administrative stuff. This reduces mail volume and ensures that
any important information is recorded in the changelog rather than being
lost.
On Mon, Jun 10, 2024 at 03:00:24PM +0300, George Stark wrote: > The situation: bootloader sets mean cpu power and mean cpu clock. > but that cpu power is not found in the voltage table (value is between table items) > due to different versions of bootloader and kernel and the regulator core sets > the minimal power but cpu clock stays the same. CPU hangs somewhere during boot. Why not just add this OPP to the table the kernel knows about? Clearly it's something the vendor set and presumably thinks the device can actually operate at. As far as I can tell you're only having problems here because you've got a software defined regulator but haven't given the software information about this configuration so it's got no idea what's going on when bootstrapping. > The core problem as I see it is if regulator is bound to CPU (or some other > complex consumer) it can't be changed except by the consumer at any stage. So > the regulator driver (core part) should wait for the own consumer to init > it properly but regulator can't be in unknown state after probing. If the regulator is configured outside the constraints configured for it in the binding then the core will bring the regulator within those constraints, some systems with regulator configurations fixed in silicon rely on this for correct performance. Regulators with unreadable hardware are very much an edge case when it comes to this, what works for one system will be broken for another one so we just have to pick a behaviour that will hopefully work more often than it breaks. We can't rely on consumers setting a voltage since consumers are only expected to set a voltage if they are actively managing it at runtime, other consumers should rely on system configuration.
Hello Mark Thanks for the review. Sorry about the separate cover-letter. On 6/10/24 18:37, Mark Brown wrote: > On Mon, Jun 10, 2024 at 03:00:24PM +0300, George Stark wrote: > >> The situation: bootloader sets mean cpu power and mean cpu clock. >> but that cpu power is not found in the voltage table (value is between table items) >> due to different versions of bootloader and kernel and the regulator core sets >> the minimal power but cpu clock stays the same. CPU hangs somewhere during boot. > > Why not just add this OPP to the table the kernel knows about? Clearly > it's something the vendor set and presumably thinks the device can > actually operate at. As far as I can tell you're only having problems > here because you've got a software defined regulator but haven't given > the software information about this configuration so it's got no idea > what's going on when bootstrapping. Actually we did a similar thing - we modified voltage table adding duty-cycle that was set by bootloader with fractional voltage value that is not used in opp table - just to make pwm-regulator happy. But this issue was very hard to find. Due to deviations of hardware component's characteristics some devices managed to keep working with minimal voltage till cpu opp driver got probed and appropriate voltage is restored. Other devices got stuck at different places with random errors. > >> The core problem as I see it is if regulator is bound to CPU (or some other >> complex consumer) it can't be changed except by the consumer at any stage. So >> the regulator driver (core part) should wait for the own consumer to init >> it properly but regulator can't be in unknown state after probing. > > If the regulator is configured outside the constraints configured for it > in the binding then the core will bring the regulator within those > constraints, some systems with regulator configurations fixed in > silicon rely on this for correct performance. Regulators with > unreadable hardware are very much an edge case when it comes to this, > what works for one system will be broken for another one so we just have > to pick a behaviour that will hopefully work more often than it breaks. > We can't rely on consumers setting a voltage since consumers are only > expected to set a voltage if they are actively managing it at runtime, > other consumers should rely on system configuration. Of course such a behavior should be configurable. At the other hand it may be too much changes for a corner case that's why I proposed only a warning patch just to simplify detecting the problem. Actually we already have a hint that says voltage is reset: rdev_info(rdev, "Setting %d-%duV\n", rdev->constraints->min_uV, rdev->constraints->max_uV); but there's no indication this is due to regulator device error. Should I consider adding my warning only for "system-critical-regulator" regulators (cpu power regulator is critical indeed)? Although this property is never used in mainline bindings.
On Tue, Jun 11, 2024 at 12:33:42AM +0300, George Stark wrote: > Actually we did a similar thing - we modified voltage table adding > duty-cycle that was set by bootloader with fractional voltage value that is > not used in opp table - just to make pwm-regulator happy. > But this issue was very hard to find. Due to deviations of hardware > component's characteristics some devices managed to keep working with > minimal voltage till cpu opp driver got probed and appropriate voltage is > restored. Other devices got stuck at different places with random errors. I think the diagnostics you are looking for here are in the PWM regulator driver. The core does announce that it's bringing the voltage into range when it does it so there's a hint that the voltage got changed there. > Of course such a behavior should be configurable. At the other hand it may > be too much changes for a corner case that's why I proposed only a > warning patch just to simplify detecting the problem. > Actually we already have a hint that says voltage is reset: > rdev_info(rdev, "Setting %d-%duV\n", > rdev->constraints->min_uV, > rdev->constraints->max_uV); > but there's no indication this is due to regulator device error. The issue is that it may not be an error, it may be normal operation - there are some regulators (those for some of the Qualcomm firmware controlled devices for example) which are purely write only so we've got no way to tell what the current configuration is and always need to write out what we want during startup. > Should I consider adding my warning only for "system-critical-regulator" > regulators (cpu power regulator is critical indeed)? Although this property > is never used in mainline bindings. To the extent that it's an issue it's going to depend on the specific regulator, the driver for a given regulator is best placed to know if being able to read back from the hardware is expected and if it should complain about not being able to.