linux-kernel - Re: [RESEND PATCH v3 1/2] drivers: amba: Updates to component identification for driver matching.

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Date:   Fri, 25 Jan 2019 10:42:23 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     mike.leach@...aro.org, saiprakash.ranjan@...eaurora.org
Cc:     linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        mathieu.poirier@...aro.org, rnayak@...eaurora.org,
        vivek.gautam@...eaurora.org, sibis@...eaurora.org
Subject: Re: [RESEND PATCH v3 1/2] drivers: amba: Updates to component
 identification for driver matching.

Mike,

On 25/01/2019 10:37, Mike Leach wrote:
> Hello Sai
> On Fri, 25 Jan 2019 at 07:20, Sai Prakash Ranjan
> <saiprakash.ranjan@...eaurora.org> wrote:
>>
>> Hi Mike,
>>
>> Thanks for the patch.
>>
>> BTW somehow I can't find the latest series in my inbox, so commenting
>> on this here.
>>
>> Mathieu pointed me to this patch series.This solves CPU debug module
>> sharing same PID as ETM on MSM8996. I will be posting patch for CPU
>> debug UCI table soon.
>>
>> But please find my one comment inline.
>>
>> On 12/19/2018 3:29 AM, Mike Leach wrote:
>>> The CoreSight specification (ARM IHI 0029E), updates the ID register
>>> requirements for components on an AMBA bus, to cover both traditional
>>> ARM Primecell type devices, and newer CoreSight and other components.
>>>
>>> The Peripheral ID (PID) / Component ID (CID) pair is extended in certain
>>> cases to uniquely identify components. CoreSight components related to
>>> a single function can share Peripheral ID values, and must be further
>>> identified using a Unique Component Identifier (UCI). e.g. the ETM, CTI,
>>> PMU and Debug hardware of the A35 all share the same PID.
>>>
>>
>> [..]
>>
>>> +static const struct amba_id *
>>> +amba_lookup(const struct amba_id *table, struct amba_device *dev)
>>> +{
>>>        while (table->mask) {
>>> -             ret = (dev->periphid & table->mask) == table->id;
>>> -             if (ret)
>>> -                     break;
>>> +             if (((dev->periphid & table->mask) == table->id) &&
>>> +                     ((dev->cid != CORESIGHT_CID) ||
>>> +                      (amba_cs_uci_id_match(table, dev))))
>>
>> Shouldn't the check be (dev->cid == CORESIGHT_CID) ?
>> Without this STM fails to probe on both SDM845 and MSM8996.
>>
> I believe the test is correct
> 
> To expand the logic here:
> 
> if  (dev->periphid & table->mask) == table->id) {
>        //** match on peripheral ID at this point
>       if (CID != CORESIGHT_ID)
>                 return table; //** not coresight - match on peripheral ID only
>       //** or
>       if (amba_cs_uci_id_match() )
>                  return table;  //** is coresight - match on UCI if
> available - otherwise peripheral ID only;
> 
> However - looking at the coresight STM driver - this is using the
> private .data field in the amba_id for a name - which I had not
> spotted before.

Good point. We also use this field for Coresight SOC-600 ETR for
advertising the caps not detected from hardware.

> I will have to revisit this patchset to fix either the amba id struct
> or the method for getting the uci data into the amba_id.data which
> allows for multiple uses.

Thanks Mike !

Cheers
Suzuki