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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