Voltage control on Southern Island GPU using radeon driver

[Christian König]

Hi Evans,

in general the voltage tables are stored in the atombios and the best 
advice I can give you is to first double check if there isn't an updated 
BIOS for your hardware.

But Alex is the expert on power management, especially for those older 
hardware generations. Maybe he has another idea what to try.

Regards,
Christian.

Am 23.08.21 um 03:56 schrieb Evans Jahja:
> Hi, I have a HAINAN GPU below:
>
> lspci -nn
> 0a:00.0 Display controller [0380]: Advanced Micro Devices, Inc. 
> [AMD/ATI] Sun LE [Radeon HD 8550M / R5 M230] [1002:666f]
>
> I run linux 5.13.12 on Arch on a Lenovo B40-70 laptop.
>
> I'm trying to understand more on how voltage control works and how I 
> can modify the voltage for doing overvoltage / undervoltage on my GPU. 
> The reason is I am observing how running programs under high GPU load 
> (glmark2) would lead to crashes when I use dpm=1 in either radeon or 
> amdgpu driver, which seems to happen when I am reaching power level 4 
> (sclk 900MHz), while a lighter program like glxgears could run and 
> switch power levels  between 0,1,2 without issue under both drivers. I 
> believe my laptop might be faulty, but I would like to take this 
> opportunity to try fixing it from the driver's side so that it can run 
> anyway, however limited.
>
> Right now, I have managed to increase the performance of my GPU by 
> manually overwriting the sclk to 630MHz in all performance_levels in 
> radeon_pm.c, which surprises me as overriding the clock was not 
> possible for me to do previously via sysfs.
>
> I've managed to tweak both sclk and mclk (or so I believe), but I 
> still cannot tweak the voltage (vddc). The reason is, if I increase 
> the sclk to 650MHz, the lockup will happen again. Changing the 
> pl->vddc  variable does not seem to do anything. After various tracing 
> with printk, I understand that on my system:
>
> pi->voltage_control = radeon_atom_is_voltage_gpio(rdev, 
> SET_VOLTAGE_TYPE_ASIC_VDDC,
>    VOLTAGE_OBJ_GPIO_LUT)
>
> this returns false, while:
>
> si_pi->voltage_control_svi2 =
> radeon_atom_is_voltage_gpio(rdev, SET_VOLTAGE_TYPE_ASIC_VDDC,
>    VOLTAGE_OBJ_SVID2);
>
> This returns true, so I believe my system is using SVI2 somehow to set 
> the voltage. Having no experience with SVI2, I read online and found 
> out that SVI2 is a voltage regulator that uses Data / Clock pins to 
> clock-in 8 bits of information and convert it to some voltage value 
> between OFF, 0.5V -> 1.5V, offering fine control based on some look up 
> table.
>
> My questions are as follows:
> Is it possible for me to modify my system so that I can manually 
> adjust the voltage to my GPU?
>
> Thank you very much in advance. This is the first time I deal with 
> kernel drivers, so any guidance on the matter helps a lot.
>
> - Evans
>
>