On 1/31/2024 5:49 AM, Bjorn Andersson wrote:
On Tue, Jan 30, 2024 at 05:00:28PM -0600, Bjorn Andersson wrote:
On Mon, Jan 22, 2024 at 10:47:03AM +0200, Abel Vesa wrote:
From: Jagadeesh Kona <quic_jkona@xxxxxxxxxxx>
Add support for set and get hwmode callbacks to switch the GDSC between
SW and HW modes. Currently, the GDSC is moved to HW control mode
using HW_CTRL flag and if this flag is present, GDSC is moved to HW
mode as part of GDSC enable itself. The intention is to keep the
HW_CTRL flag functionality as is, since many older chipsets still use
this flag.
This provides insight into why we end up with both HW_CTRL and
HW_CTRL_TRIGGER. This doesn't describe why this change is needed, but
rather just an implementation detail.
But consumer drivers also require the GDSC mode to be switched dynamically
at runtime based on requirement for certain usecases. Some of these
usecases are switching the GDSC to SW mode to keep it ON during the
enablement of clocks that are dependent on GDSC and while programming
certain configurations that require GDSC to be ON. Introduce a new
HW_CTRL_TRIGGER flag to register the set_hwmode_dev and get_hwmode_dev
callbacks which allows the consumer drivers to switch the GDSC back and
forth between HW/SW modes dynamically at runtime using new
dev_pm_genpd_set_hwmode API.
This still expresses the need for HW_CTRL_TRIGGER in terms of "some
drivers need for some use case". We don't need these many words to say:
"Introduce HW_CTRL_TRIGGER for client drivers that need it."
I find that it would be useful to document that every time a GDSC is
turned on the mode will be switched to SW...
I believe I'm wrong here. Reading the patch again, I think we might
retain the mode across a disable/enable cycle. I at least don't see
anything explicit returning us to SW mode.
> According to Linux though, the GDSC is off, so as described below, there
will be no votes for supplying resources.
Yes, With HW_CTRL_TRIGGER flag, the GDSC mode gets switched only in new
set_hwmode_dev() callback when consumers explicitly call for it. This is
to ensure GenPD f/w's hwmode aligns with the actual GDSC mode in HW.
With the new API, the expectation is consumer drivers should move the
GDSC to SW control mode before disabling the GDSC, which ensures that,
GDSC is turned ON in SW mode every time.
Thanks,
Jagadeesh
Regards,
Bjorn
