Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections

[Sai Prakash Ranjan]

Hi Mike,

On 2020-05-13 03:22, Mike Leach wrote:

[...]

> Looking at the AMBA driver there is a comment there that AMBA does not
> lose state when clocks are removed. This is consistent with the AMBA
> protocol spec which states that AMBA slaves can only be accessed /
> read / write on various strobe signals,  or state reset on PRESET
> signal, all timed by the rising edge of the bus clock. state changes
> are not permitted on clock events alone. Given this static nature of
> AMBA slaves then removing the clock should not have any effect.
>
> The AMBA driver only /drivers/amba/bus.c  gives permission to
> remove/restore the clocks from the devices (pm_suspend pm_resume
> callbacks) - this reduces the power consumption of these devices if
> the clock is not running, but state must be retained.

Thanks for the clarification.

> > >> >>
> > >> >> pid=0x2bb909 for both replicators. So part number is same.
> > >> >> UCI will be different for different implementation(QCOM maybe
> > >> >> different from ARM),
> > >> >> but will it be different for different replicators under the same
> > >> >> impl(i.e., on QCOM).
> > >> >
> > >> > May be use PIDR4.DES_2 to match the Implementor and apply the work
> > >> > around for all QCOM replicators ?
> > >> >
> > >> > To me that sounds the best option.
> > >> >
> > >>
> > >
> > > I agree, if it can be established that the register values that make
> > > up UCI (pid0-4, devarch, devtype, PID:CLASS==0x9), can correctly
> > > identify the parts then a flag can be set in the probe() function and
> > > acted on during the enable() function.
> > >
> >
> > So here I have a doubt as to why we need to use UCI because PID =
> > 0x2bb909
> > and CID = 0xb105900d are same for both replicators, so UCI won't
> > identify the
> > different replicators(in same implementation i.e., on QCOM) here.
> > Am I missing something?
> >
> > Thats why I think Suzuki suggested to use PIDR4_DES2 and check for 
> > QCOM
> > impl
> > and add a workaround for all replicators, something like below: (will
> > need cleaning)
> >
> > #define PIDR4_DES2      0xFD0
> >
> > if (FIELD_GET(GENMASK(3, 0), readl_relaxed(drvdata->base + 
> > PIDR4_DES2))
> > == 0x4)
> >         id0val = id1val = 0xff;
>
> Please look at the CoreSight components specification 3.0 (ARM IHI
> 0029E) Section B2.1.2 which describes the Unique Component Identifier
> (UCI).
> As mentioned above this consists of a combination of bits from
> multiple registers, including PIDR4.

Ok got it now, thanks for clearing the doubt. I will go ahead with
this method to identify QCOM impl and post a patch.

Thanks,
Sai

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