Re: [PATCH 1/4] media: qcom: camss: clamp VFE clock rates to the highest level

[Gjorgji Rosikopulos (Consultant)]

Hi Atanas, Loic, All,

On 10/23/2026 6:50 PM, Atanas Filipov wrote:
> On 10/23/2026 6:45 PM, Loic Poulain wrote:
>> On Fri, Oct 23, 2026 at 5:29 PM Atanas Filipov
>> <atanas.filipov@xxxxxxxxxxxxxxxx> wrote:
>>>
>>> The VFE fails to power on when the pixel rate exceeds the highest rate
>>> listed for any of its clocks. The rate tables of the VFE clocks are
>>> independent and need not have the same number of levels, so a clock
>>> with a lower top rate than the VFE core clock, such as the SC7280
>>> camnoc_axi clock, makes the VFE reject pixel rates the core clock
>>> still supports.
>>>
>>> Clamp each clock to its highest listed rate instead, and warn that the
>>> pixel rate exceeds it when the clock lists more than one rate. Take the
>>> clamp into account when another line powers on an already running VFE,
>>> so that a clock running at its highest rate does not reject the
>>> request.
>>
>> IMO, this function has become a bit messy. We should split the core
>> clock selection into a dedicated helper, as it is directly tied to the
>> pixel rate. The AXI clock scaling/selection should be handled
>> separately, potentially through the interconnect (ICC) framework (when
>> available).
>>
>> Regards,
>> Loic
>>
> 
> I completely agree. I just don't want to mix the two issues, as 
> requested by the reviewers. IMO, if we can reach an agreement on the ICC 
> migration, that would be great.
> 
> Regards,
> Atanas
> 

There have been several discussions about this topic. 
I would like to summarize the background here and reopen the discussion
about the direction proposed by Atanas.

The issue initially came up with the JPEG encoder driver, which is
represented as a separate device. Dmitry identified that changing the
camnoc_ax clock from the JPEG driver conflicts with CAMSS.
I will not revisit the discussion about why JPEG is not part of CAMSS, 
as this has already been discussed extensively.

Currently, CAMSS is represented as a single device and drives the front-end
blocks that write data to memory, such as VFE, IFE, and TFE.

Depending on the hardware architecture, CAMSS may contain different number
of front-end blocks. Some camera subsystems also contain offline engines
like JPEG and OPE.
All these engines write data to memory through the internal CAMNOC and
share the camnoc_axi clock.

The relevant topology can be summarized as follows:

CAMSS device: Front end -> CAMNOC -> MNOC
OPE device: OPE -> CAMNOC -> MNOC
JPEG device: JPEG -> CAMNOC -> MNOC

An ICC path is already available for MNOC, and each device can vote on it.

CAMSS currently has two issues on this topic that need to be addressed.

1. Clock aggregation for concurrent streaming, As described in the cover
letter, CAMSS currently does not aggregate the clock requirements when
multiple front-end engines are streaming concurrently.

2. ICC bandwidth voting
The currently available MNOC ICC voting is implemented using max bandwidth
values. This can increase power consumption in single-camera use cases.
This is not included in this patchset.

Addressing the first issue depends, to some extent, on the direction we
choose for CAMNOC ICC support. Atanas has proposed two possible approaches.

1. [PATCH v2 0/3] Add Qualcomm CAMNOC ICC provider

The patchset adds an initial CAMNOC ICC provider with multiple ports, where
each port represents an engine client of the CAMNOC.

This allows a device such as CAMSS, which is represented as a single device,
to vote independently through different CAMNOC ports. The CAMNOC ICC provider
can then aggregate the votes and calculate the appropriate camnoc_axi clock
rate.

1. [PATCH v3 0/3] Use icc-clk for the SM8250 camera NoC AXI clock

The ICC framework, together with CAMCC support, can represent a clock as an
ICC provider. The implementation is relatively simple because it reuses the
existing infrastructure, the camnoc_axi clock only needs to be exposed as an
ICC provider.

The limitation of this approach is that a device such as CAMSS cannot vote for
each engine independently.

I think the patchset should be updated based on the approach we agree to use.
If there are other possible solutions, please share them here as well.

Apologies if this message is not perfectly structured. But i think is
understandable. 

~Gjorgji