linux-kernel - Re: [PATCH] coresight: etm4x: Enable ETE device accessed via MMIO

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Date:   Thu, 19 Oct 2023 14:41:55 +0800
From:   Ruidong Tian <tianruidong@...ux.alibaba.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-kernel@...r.kernel.org
Cc:     james.clark@....com, coresight@...ts.linaro.org,
        mike.leach@...aro.org, alexander.shishkin@...ux.intel.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] coresight: etm4x: Enable ETE device accessed via MMIO

Hi Suzuki

You are right, I review armv9 Spec again, and find that ETE only
support system instructions access.  This patch is meaningless and
need to drop it.

Ruidong

在 2023/10/18 17:36, Suzuki K Poulose 写道:
> Hi
>
> On 18/10/2023 10:30, Ruidong Tian wrote:
>> Hi Suzuki,
>>
>> Now ETM4X driver use MMIO or system instruction depends on this check 
>> in function etm4_init_csdev_access:
>>
>>          if (drvdata->base)
>>                  return etm4_init_iomem_access(drvdata, csa);
>>
>> This check always true if firmware provides a address range in ACPI
>> table of ETE, and as a result, the ETE device in this case cannot be
>> successfully probed.
>>
>> I think OS should be compatible with this situation, no matter firmware
>> how to organize ETE information in ACPI table. How do you feel about
>> it?
>
> My question is not about "What the patch does". But, why can't we use
> system instructions on your system, when ETE was designed to be used
> with that in the first place and get rid of the MMIO.
>
> Suzuki
>
>>
>> Thank you
>>
>> Ruidong Tian
>> 在 2023/10/18 16:28, Suzuki K Poulose 写道:
>>> On 18/10/2023 08:05, Ruidong Tian wrote:
>>>> The ETM4X driver now assume that all ETE as CPU system instructions
>>>> accessed device, in fact the ETE device on some machines also accessed
>>>> via MMIO.
>>>>
>>>> Signed-off-by: Ruidong Tian <tianruidong@...ux.alibaba.com>
>>>
>>> Why are we going backwards to MMIO from system instructions ? Is it 
>>> because of an "unfriendly" hypervisor preventing access ?
>>>
>>> As such, without a sufficiently acceptable explanation, I am reluctant
>>> to make this change
>>>
>>> Suzuki
>>>
>>>> ---
>>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 5 +++--
>>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c 
>>>> b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> index 285539104bcc..ad298c9cc87e 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> @@ -1103,8 +1103,9 @@ static bool etm4_init_iomem_access(struct 
>>>> etmv4_drvdata *drvdata,
>>>>        * with MMIO. But we cannot touch the OSLK until we are
>>>>        * sure this is an ETM. So rely only on the TRCDEVARCH.
>>>>        */
>>>> -    if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH) {
>>>> -        pr_warn_once("TRCDEVARCH doesn't match ETMv4 
>>>> architecture\n");
>>>> +    if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH &&
>>>> +        (devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETE_ARCH) {
>>>> +        pr_warn_once("TRCDEVARCH doesn't match ETMv4/ETE 
>>>> architecture\n");
>>>>           return false;
>>>>       }