Re: [PATCH V6 0/6] coresight: etm4x: Migrate ACPI AMBA devices to platform driver

[Suzuki K Poulose]

On 26/07/2023 18:03, Steve Clevenger OS wrote:
> Hi Suzuki,
>
> On 7/26/2023 9:59 AM, Suzuki K Poulose wrote:
> > On 10/07/2023 07:24, Anshuman Khandual wrote:
> > > CoreSight ETM4x devices could be accessed either via MMIO (handled via
> > > amba_driver) or CPU system instructions (handled via platform driver).
> > > But
> > > this has the following issues :
> > >
> > >     - Each new CPU comes up with its own PID and thus we need to keep on
> > >       adding the "known" PIDs to get it working with AMBA driver. While
> > >       the ETM4 architecture (and CoreSight architecture) defines way to
> > >       identify a device as ETM4. Thus older kernels  won't be able to
> > >       "discover" a newer CPU, unless we add the PIDs.
> > >
> > >     - With ACPI, the ETM4x devices have the same HID to identify the
> > > device
> > >       irrespective of the mode of access. This creates a problem where two
> > >       different drivers (both AMBA based driver and platform driver) would
> > >       hook into the "HID" and could conflict. e.g., if AMBA driver gets
> > >       hold of a non-MMIO device, the probe fails. If we have single driver
> > >       hooked into the given "HID", we could handle them seamlessly,
> > >       irrespective of the mode of access.
> > >
> > >     - CoreSight is heavily dependent on the runtime power management. With
> > >       ACPI, amba_driver doesn't get us anywhere with handling the power
> > >       and thus one need to always turn the power ON to use them. Moving to
> > >       platform driver gives us the power management for free.
> > >
> > > Due to all of the above, we are moving ACPI MMIO based etm4x devices
> > > to be
> > > supported via tha platform driver. The series makes the existing platform
> > > driver generic to handle both type of the access modes. Although existing
> > > AMBA driver would still continue to support DT based etm4x MMIO devices.
> > > Although some problems still remain, such as manually adding PIDs for all
> > > new AMBA DT based devices.
> > >
> > > The series applies on 6.5-rc1.
> > >
> > > Changes in V6:
> > >
> > > - Rebased on 6.5-rc1
> >
> > I have queued this version for v6.6, should appear on coresight/next soon.
> >
> > Suzuki
>
> Is there anyway to queue this for 6.5? Or has that ship sailed?

Only fixes are allowed for v6.5 at this time.

Suzuki

> Thanks,
>
> Steve C.