Re: [PATCH 3/3] clk: qcom: Set BRANCH_HALT_DELAY flags for venus core0/1 clks

From: Stanimir Varbanov
Date: Mon Dec 12 2016 - 10:40:44 EST

Hi Stephen,

On 11/09/2016 12:33 AM, 'Stephen Boyd' wrote:
> On 11/07, Rajendra Nayak wrote:
>> On 11/05/2016 01:48 AM, 'Stephen Boyd' wrote:
>>> Well I'm also curious which case is failing. Does turning on the
>>> clocks work after the gdsc is enabled? Does turning off the
>>> clocks fail because we don't know when the gdsc has turned off? I
>>> would hope that the firmware keeps the gdsc on when it's done
>>> processing things, goes idle, and hands back control to software.
>>> Right now I'm failing to see how the halt bits fail to toggle
>>> assuming that firmware isn't misbehaving and the kernel driver is
>>> power controlling in a coordinated manner with the firmware.
>> What fails is turning ON the clocks after the gdsc is put under
>> hardware control (by fails I mean the halt checks fail to indicate
>> the clock is running, but register accesses etc thereafter suggest
>> the clocks are actually running)
>> The halt checks seem to work only while the gdsc is put in SW enabled
>> state.
> Um... that is bad. I don't see how that is possible. It sounds
> like the clocks are not turning on when we're asking for them to
> turn on. The register accesses are always working because these
> subcore clks aren't required for register accesses. Most likely
> the GDSC for the subdomains is off (even after we thought we
> enabled it).
> Let's take a step back. The video hardware has three GDSCs. One
> for the main logic, and two for each subdomain. We're adding hw
> control for the two subdomains here. From what I can tell there
> isn't any hw control for the main domain. I see that there are
> two registers in the video hardware to control those subdomain hw
> enable signals that go to the GDSC. The reset value is OFF (not
> ON like was stated earlier), so it seems that if we switch the
> subdomain GDSCs on in these patches it will turn on for a short
> time, and then turn off when we switch into hw mode (by virtue of
> the way we enable the GDSC). Presumably we can assert these hw
> signal bits regardless of the subdomain power states, because
> otherwise we're in a chicken-egg situation for the firmware
> controlling this stuff.
> The proper sequence sounds like it should be:
> 1. Enable GDSC for main domain
> 2. Enable clocks for main domain (video_{core,maxi,ahb,axi}_clk)
> 3. Write the two registers to assert hw signal for subdomains
> 4. Enable GDSCs for two subdomains
> 5. Enable clocks for subdomains (video_subcore{0,1}_clk)

Do you think this sequence 'enable GDSC and the clocks behind it' is
valid for MMAGIC GDSCs too?

2. Enable clocks (not sure which they are) -
3. Continue with the sequence above.